The way you ask your psychiatrist about it is the same way you just asked me about it! Good job for asking.
Gabapentin in the treatment of panic disorder and GAD is 'off label', meaning, it was not what the medicine was created to do (it was created to treat seizures), but, as often happens, doctors have discovered that it has other uses too. One is the treatment of chronic nerve pain, and another is in a cases such as yours where it is part of the medication regimen used to control your symptoms.
Also, there is a maximum dose of 1800mg per day, and right now you are taking half of that, so there is some room to move on the dose, but only your prescribing physician can make that call.
I think your question is an excellent one, and it is one I would think your psychiatrist would be pleased to answer for you. Remember, your psychiatrist works for YOU. They are there to help YOU. There is no reason to fear asking your doctor about this, but then I understand that your GAD is a difficult thing to deal with.
I would place a call to your psychiatrist's office and ask to speak or meet with him/her as soon as you can about a possible medication modification.
Please let me know if you have questions about my answer.
Positive feedback is always appreciated.