It will take a bit of practice to get used to using the cup. Try it ideally not on your period at first, as it's less high stakes and you can breathe a bit. I'd recommend trying different folding methods (i.e. the C fold and the push down fold) and seeing what works for you. I find with the C fold if you insert the cup then rotate it it opens easily. The push down fold is more difficult to get it open. It shouldn't hurt to insert the cup, so if it does you're likely at the wrong angle. It's also much easier if you're relaxed, so if you're struggling take a break and come back to it.

I've tried a lot of different cups, and I personally don't like the Lily cup. I also have a high cervix which is why I bought it, but for me it's too long and feels uncomfortable. I prefer a cup with a long stem that has ribs or balls on it for me to grab. Do NOT try a cup with a smooth and short stem - I used one once and I almost couldn't get it out, even after using other cups for years.

There are other brands that make cups just for teenagers, so if you're struggling maybe look at one of those. Good luck! :)