Should I be concerned I'm pregnant?

So I'm 17, a senior in high school and I stopped taking birth control pills because they gave me such burdensome anxiety and depression that I couldn't function. Of course, because of the change my boyfriend and I always use a condom. I went to see him at college (he's 18, a freshman) and we used a condom but when he came his cum somehow came out of the top of the condom (as in the end of his shaft) while he was cumming and thrusting still a few times. I freaked out after because I've never had to worry about being pregnant so much if a condom breaks because I've always been on the pill until now. We rushed to RiteAid directly after (like literally 20 minutes after it happened) and I took Plan B. I hear that if you have a BMI over 25 Plan B won't work for you, and I have a BMI of 26.6 so I'm incredibly worried. Should I still be this worried? This was the ONLY time this month that we had sex and the condom failed. What are my odds of becoming pregnant?