Please read and help me.No jokes Please?

i had unprotected with a girl whose hiv status i don't know.It was my first time and i had masturbated before doing ,then i put my **** in her ****** and it was not even 30 seconds that i d and we stopped.Before this when i fingered her ****** it was not wet really.So after a week i got tested for hiv PCR test and it showed negative.Then after 14 days ie 15th day i retested for hiv PCR test and it was negative again.So i wanted to ask how conclusive are my results after 14 days?As i am being told that the PCR test is a detailed one and it looks for even a small micro particles in blood.Please Help me I am really very scared and will never ever in my life do such a stupid thing.I am really worried.