First ultrasound and so confused!

Ashley • Married to the love of my life! Baby Jack 1/2/16! Baby Brody 8/26/18!💙💙
Ok answer this girls!
Went in for my first ultrasound today and I had been using OPK's and my cycle was like 100% regular. Anyway I got my peak day on May 5th so implantation must have happened a weekish later. Well today the ultrasound tech tells us I'm not 9w2d I'm actually 10w2d a whole week ahead! How is that possible?? I mean that's fine less waiting for me, but should I be scared I'm going to have a giant baby or is that pretty possible?? 
Ps NOT trying to rub anything in because you girls will be here with me next month for sure!! 😀