Not sure hun, but I would invest in a pregnancy test if I were you just in case (stranger things have happened) and maybe even if it's negative still book in to see a GP xo
I don't know the failure rate, but my mum actually got pregnant when I was a teenager after having had a sterilisation (clips) but unfortunately it was an ectopic pregnancy that ended up being caught very late because the drs didn't think to check for pregnancy after sterilisation. It was my mum that caught it in the end because she did a home pregnancy test that was positive.
Would definitely recommend you get checked out if you think it's a possibility.
Good luck It's probably really unlikely anyway, but it's always worth getting checked out just in case and to put your mind at rest