Can a yolk sac show up in a ultrasound 4 days after unprotected ?

I'm 17 years old, and apparently don't know much about pregnancy. Me and my boyfriend had 3 days ago and the condom broke, but we didnt realize it until he 'went' then pulled out. We think a little peice of the condom may be still inside of me. Can this harm my body if i dont get it taken care of? After we discovered this scare of my life, i took the Plan B pill. Also, i have a pelvic sonogram tomorrow and i want to know if Anything would come up that the doctor can see that i might be pregnant. Please help me with some answers as soon as possible. Thank You!