Please say a prayer for me
Putting off something because you are afraid just lets you be afraid longer. I assume you want to be with this girlfriend no matter what, and finding out (in the case of the news being that you are not the dad) is not going to drive you away? For heaven's sake, find out.
Call the family courts in your area of jurisdiction and ask what lab the courts have certified for determining paternity. Don't do a drugstore test, go to a certified lab where they request ID and the samples are handled by techs and all. She should test with you and the other guy if he will test, your all deserve a clear yes on one guy and a clear no on the other.
Because the baby measured small during her pregnancy I am not thinking the margin for error of the ultrasound extended back to the sex March 20. But the only way to know absolutely is to test.
Some lady saying her baby was 19 days late and was only 6 lbs. 12 ounces is not proof of anything regarding your girlfriend's baby. (Or even actually regarding her baby either ... how did the lady know she was 19 days late, did the doctor scan her ovaries with an ultrasound every day to determine when she ovulated? How big are the people in her family and in her husband's family? How was her nutrition when she was pregnant? How important was it to her to say that because her husband was gone at the time the baby would actually have been conceived? etc. You don't know her motives or what proof she had.)
More to the point, my husband commented recently on how little the genetic package of a child means compared to the lengthy, interesting and involving effort of raising one. He said it's "a blink of a gnat's eye" what creates the child compared to raising one, and our son is only 10. We've got years to go! If you care about this girl, and want to be involved, be involved. A genetic connection is not the be-all and end-all.
The sonogram being that late doesn't give him a strong chance though? It worries me because I heard a lady say she had a baby 19 days late at only 6lb. 12 ounces. I'm going to do a paternity test but I wanna know my chances, but I also don't want to have my hopes up. The only reason I've put it up this far is because the baby doesn't look that much like me and I'm afraid.
Because her first due date, November 22, gives a conception date of March 1, and even if it was a later ultrasound the baby was measuring small, not large, during the pregnancy, and the baby was not overly large when born on November 25. All of those things suggest she didn't get pregnant much before March 1.
Why do you think I am? I hope you are right
Sounds like you are the dad. Get a DNA test and put the worries behind you.