My Lmp Was 26:07:15 Which Lasted 5days. I Had Regular

My lmp was 26:07:15 which lasted 5days. I had regular sex on the 8, 9, 10 & 12:08:15 in preparing for pregnancy with my husband. I had an ultrasound on 10:09:15 which measured 6w 3 days (crl.64cm), how accurate are dating ultrasounds? I have a 29-30 day cycle and had sex with a different guy at 6:00pm on 11:08:15 using a condom that recently confessed to me that he bore a small hole in the condom and some little amount semen went in me. I am frantic now because I am 26w 6d pregnant today and worried that it might not be my husbands child. I am scared out of my wits. Can I trust the crl measurements at 6 weeks 4 days?