Are you on your period now? If you are it might be worth waiting a bit, and then trying it when you arent on your period, just try to stay calm and relaxed and try later. And as was siad - bigger things can go up there!
From the FAQ: Okay, I have a mooncup and I’m having problems. I’m finding it really hard to get in.
I think nerves play a big part in this. Relaxation is key. The good thing about mooncup is that you can practice any time with it, because it doesn’t dry you out. Failing practice, try a little WATER BASED!!! Lubricant to help you pop it up there. Remember to fold it as tightly as possible.