Possible pregnancy?

Hi everyone. I had sex 2 days ago, we used a condom but it started slipping off but he stopped and took it off before anything could happen and before that he had his penis on my vaginal opening without a condom. eve is saying that I was not ovulating. I took a Plan B in case pre cum got in me from him being on my vaginal opening/hole. My periods are irregular, I should be getting my period anywhere between June 18-24 and will be ovulating in 5 days. I have 3 questions.

- Could I get pregnant from his penis being on my hole? He then put a condom on and we had sex, so could the pre cum go in then?

- Was Plan B needed for the condom slip?

- How effective is Plan B? I took it within 30 hours

I know I should get birth control, but it’s not that easy for me due to certain conditions. I’m stressing out so much, I just want to know if my worrying is reasonable or I’m completely okay. Thank you so much.