Nobody can say you have nothing to worry about. It's always possible. No sex is safe sex. There have been women who have gotten pregnant while on b/c and using condoms. It's not likely but it does happen.
it is unlikely, if you used a condom and it didnt break, and you removed your penis before removing the condom, it is very unlikely that your girlfriend will be pregnant, the substance you saw on the shaft of your penis may well have been from her, this is very common, I dont htink you have anything to worry about :)
Any time you have sex there is a risk of pregnancy. The only thing you can do (it's too late for plan b) is to wait and see if her period starts. If it doesn't she needs to take an hpt.