I am not on birth control. the condom slipped off last night and was inside my vagina. he had not came, pulled condom out. need plan b?

Gamble.: If you want to be sure you are not pregnant then Plan B is a good choice. If you want to be pregnant then doing nothing is reasonable.

Risk: Even if he had not ejaculated, there may have been release of pre-ejaculate. Sometimes pre-ejaculate still contains viable sperm. Thus, there is still some level of risk. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours.