I bought plan b but it fell in the sink before eating. it melted just a little but i still ate it. will this work? or can i take another one within 72 hours?

If the majority of the "Plan B" was available for ingestion, it will work to the limit of its ability, but while "taking another" is OK, remember that Plan B is not 100% effective in preventing pregnancy. If your period is delayed, obtain a serum HCG test to be certain about pregnancy.

It is unlikely that fall in the sink will reduce the effectiveness of the pill. Plan B, taken within 72 hours of sex is about 95% effective. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex : https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines Get HPV vaccine.