I Have A Girl Telling Me That She Is Pregnant.

I have a girl telling me that she is pregnant. It has only been four days since we had unprotected sex and we did it once. She sent me pics of a positive urine test and she said she tested positive on the blood test. Also, she sent me a pic of an ultrasound showing a gestational sac. My question is: is there any way that she could have got pregnant by me since we had sex only 4 days before she took the tests and got the ultrasound?