conception date?

I'm 22 weeks 2 days pregnant, which means I conceived on the 17th of June, which matches up perfectly to when I last slept my ex, we did split and I drunkenly slept with someone else on the 26th of June, after this I took emergency contraception which I assumed didn't work as because I must have already pregnant? is there a possibility of her actually being conceived on the 26th? All my scans she's been measuring up perfectly to her due date which is March 17th I've been so sure but I have a tiny seed of doubt, in which case I will have to explain myself and sort out a DNA test. No judgemental comments please it was completely out of character for me and naturally I am carrying enough guilt. I know no one is a dr on here but I was curious if anyone had been through something similar? 
I can't reply anonymously so I've had to add my comment here, thankyou all so much, I bit the bullet and told him the need for a DNA test anyway (it's the honest thing to do) the complication I had is 4 weeks prior to this I had an ectopic pregnancy which resulted in surgery so my cycle was disrupted, I'd actually had my Period staring the 14th of June and it had ended the 17th, which is why I stupidly didn't take any contraception. After the 26th I took emerancy contraception within 12hrs. 13th of July I had a BFP and my digital prediction test said 4-5 weeks pregnant, which meant I conceived 2-3 weeks previous, obviously they're not accurate.