Can a scan at 20 weeks be approx 10 weeks out, could I possibly only be 9 or ten weeks instead? I was with person A in August and person B in October (about 11 weeks between them) should I be concerned, can scans possibly be this far out?

No, scans will not be this far out. A week or two most certainly, but not 9 or ten weeks.

Thanks for that, I know it sounds a ridiculous question but the mind plays tricks and I can't stop thinking about the possibility that October guy is the dad even though my scan says I conceived 11 weeks prior to this.