“Could The Pregnancy Be Mine?” (Please Advice)

“Could The Pregnancy Be Mine?”

Hi guys, I will try and make the story short.

I had unprotected sex with my girlfriend on 18th of July, She told me on the 27th of August that she went for pregnancy test and she is 2 weeks pregnant.

Just kind of confused as to the disparity in the dates. The result should be 5 weeks plus (Almost 6 weeks) and not 2 weeks.

Please, to the health workers, how accurate can pregnancy test be? No problem if the pregnancy is mine but wont want to take responsibility for what is not mine.