Menstrual cup too low??

So this is the first time using my diva cup. My period started today and I waited until night time to give it a go. when I got out of the shower I put it in and at first it felt totally fine, but then it slipped down some. I can push it back up a little bit, but now the stem is always just a little bit too far out to where its uncomfortable. everytime I push it up it just moves back down when I start walking around again. I've already trimmed the stem a little bit, and when I checked my cervix I thought it was medium to high, certainly not low. Do I need a shorter cup? did I not put it in far enough when I first put the cup in? I really want this to work out! How can I fix this?