Hi, I,m Ted and I will assist you.
I will assume that replacing the injector fixed the original problem. What may have happened is when you removed the fuel rail to replace the injector, when you went to reassemble it you may have not gotten the injectors to seal in the intake. a vacuum leak from here can cause a p0300 because it can affect more than one cylinder. Did you clean the intake holes and lubricate the injector orings when you reassembled the parts.