Stain on Couch after Sex?

My boyfriend (M28) and I (F28) had sex last night. I am on Slynd birth control and I take it at the same time every day. We also always wear a condom.

After he finished I noticed that the tip of the condom was sagging a little bit but it looked like all fluid remained inside. In retrospect the condom was probably the wrong size. When I got up from the couch, I noticed that there was a small stain on the cushion where I was laying.

My boyfriend gave no indication when he was taking the condom off that it may have ripped or leaked. I feel the likelihood that something happened is relatively low, but of course I’m in my head now. Should I take a Plan B pill just in case?