uh oh

Had sex with no condom for the first half of sex (with a condom for second half) on day 23 of my cycle. On day 26 the condom broke and he came in me. I took a plan b on day 28 of my 28 day cycle. I wasn't going to take one because it was so late into the cycle but I got nervous and took one. It's now day 31 and still no period. How much should I be panicking