Plan b help

So I had sex for the first time and we were dumb and had it unprotected. I’m 15 and i don’t know if I should take a plan b just in case. He didn’t come inside me but I checked later (like 20 mins) on and saw some white mucous stuff that looked like discharge but I still have doubts. Should I take a plan b? Ps the sex was amazing 😂😂