Cup is leaking?

I am using a Flexcup and it’s been leaking. Not a lot, but enough that I need to wear a liner. It’s a little uncomfortable because I can tell when it’s leaking. I’ve taken the cup out when I notice this and it’s not even half way full. I’ve made sure the cup is fully opened up inside of me when I insert it by pushing my finger along the entire base so that can’t be it. I am using the smaller size Flexcup. Could it be that it’s too small? I haven’t given birth before. What do you all think? I can’t switch to another cup because I need the ring for release. Thanks!