On June 23rd I Found Out I Was 4-5 Weeks

On June 23rd I found out I was 4-5 weeks pregnant. On July 22nd I had an ultrasound done and the lady said I was measuring at 8 weeks 5 days. My hcg level was 170171 and the doctor told me the end result I was 8 weeks 6 days pregnant. On July 30th I had my first obgyn appointment and the doctor asked her to do a fast ultrasound less than 5 minutes long and the screen was reading 9 weeks two days. My partner and I had been trying for a baby and he threw a party on June 11th his buddy had tainted the punch and claimed to have been with me. We are just trying to make sure that I am pregnant with my partners baby and not his buddy. The prenatal dna testing is way expensive and we were both worried and considering adoption. Polive report has been filed against buddy just want to have peace of mind. And an in depth answer.