Should I buy Plan B?

Okay before I go into this just know that I have kind of severe anxiety so if this sounds stupid it's because of that.

Anyway my boyfriend and I ended up having spur of the moment sex yesterday. I'm on birth control (Nuvaring) but I'm going to have to insert it a day later than normal because I'm visiting my mom and I left it at my house in another city. My boyfriend and I used a condom and he didn't cum in me, but the condom didn't fit too well (it only went about 3/4 of the way up). I'm also on my period. I'm having pretty bad anxiety about getting pregnant because the condom didn't fit correctly and I'm going to be late taking my birth control. Should I go buy Plan B?