OK this is probably not going to be the answer you are looking for but I have to tell you the truth.
These kits that are sold in auto parts stores do more harm to the A\C system than good, First they are inaccurate and the pressure gauges they have are not the best idea. The correct way to charge the A\C system accurately is to evacuate all the current charge in the system and put the amount that the system takes and nothing more, There's no such thing as topping off the A\C system, it's not like other fluids that you top off until you get to the full mark and you're good to go. If you under charge your system then the a\c system will not cool well due to low pressures and low oil transfer will cause permanent compressor damage. If you overcharge the system will overwork the compressor and put tremendous amount of pressure on all components and one component is going to give and leak out.
The only correct way to charge the A\C system is to use a manifold gauge set and an accurate scale to measure the amount of freon you are adding, You will first need to remove all the refrigerant from the system in a process that we call Evacuating the refrigerant, You CANNOT vent refrigerant to the atmosphere since this is a violation of EPA(Environmental protection agency), You have to use a recovery tank to store the recovered refrigerant, Then place the system in a vacuum for at least 15 minutes, you are trying to get rid of any moisture in the system, moisture(water) boils when placed in a vacuum, 15 minutes is the minimum time to boil all the moisture out of the system, Then after all this you will inspect the system pressure while it's in a vacuum, if the vacuum goes to pressure then you have more refrigerant in the system and you need to repeat the steps all over, If the vacuum goes to zero then you have a leak. If it holds vacuum for at least 5 minutes then you have no leaks or at least you have no leaks that are big enough. Then you will re-add any oil that was evacuated with the refrigerant, usually A\C machines will have an oil separator so you'd know how much you pulled out of the system, You don't want to run the system low on oil. After everything checks out then you will charge the CORRECT amount of refrigerant into the system and nothing more, After this you will observe the pressures, You're looking at around 35psi on the low side and over 200 on the high side I would say indicate a good working a\c system.
The kit that you have only charges on the high side, And the gauge you have is only on the high side, Your high side could be over 200 and everything looks beautiful but the low side could be 200 as well or could be 10 you don't know until you check it. I will give you an example why this kit is not accurate, If your high side is 220psi and looking good and you think OK we're good to go but in fact the compressor is not running and the low side is 220psi as well, If the ambient temperature is 90F and you have 220 you are approximately at double the correct amount of freon!! but at the same time 220 on the high side is good?!! Exactly, that's how people ruin their A\C system and then have to pay lots and lots of money replacing major A\C components to fix the problems caused by trying to save a few bucks by doing it themselves. Please note that the A\C service at any shop doesn't cost much more than a couple cans of the Kit. If you have the right equipment then I can walk you through the process and you'll have a great working A\C otherwise better be safe than sorry have a professional shop with the right equipment recharge your A\C system and save yourself the headaches.
The correct equipment needed to properly service your a\c system are a set of manifold gauges, A vacuum pump,a digital scale and a recovery tank. Please note that you have to be certified by the EPA to work on A\C systems due to the dangers and possible harm to the environment when working with refrigerant.
Like I stated this might not be the answer you'd like to hear but I am trying to help with honesty, If you choose not to trust what I am trying to tell you then I'd like to give you some pointers and precautions to take when working with the kit. Please do not vent refrigerant to the atmosphere, The EPA will issue fines if they find you doing this. Please DO NOT touch the refrigerant in case you have a leak, if you touch refrigerant you will have a frost bite that is serious and you should go to the hospital immediately. Don't blow up your A\C system by overcharging it as this will cause MAJOR injury and damage to your vehicle. Then refer to the Pressure\Temperature chart, Charge ONLY with the A\C off and measure the ambient temperature which is the temperature in front of the condenser, Work with the vehicle cold and your pressure on the little gauge in the kit should be the equivalent to the ambient temperature from the kit, That is in no way accurate but it's as close that you are going to get with the kit. You may find the chart at this link : http://www.mexichemfluor.com/americas/download/Mexichem%20KLEA134a%20P-T%20Chart%20Final.pdf
Please be careful when handling refrigerant.
If you have any other questions please let me know, I am here to help.