Very unlikely you were infected. Dont worry and test at 3 months
Well by medical consensus 4-6 weeks post-exposure would yield a RELIABLE result, but not yet conclusive. And if the tested is on chemotherapy, on meds after organ transplant, or a heavy drugs user, the conclusive testing period becomes 6 months since they all delay the HIV antibody level to be detectable.
but i have heard window period lasts from 4-6 weeks and above that it is very rare...as it is reserved for those who are on drugs and have supressed immune system...am i right?
If it was vaginal and/or anal and without condom or the condom broke (which would've been visible), then get yourself tested at 3 months post-exposure. The girl could've got HIV earlier and passed it you and by the time of the testing she could've been still in window period.