Help!!!

I just recently started my period and want to have an eco-friendly period for the rest of my life. I tried to put my diva cup in today and I honestly don’t understand how that large of a cup can fit into that small of a hole (I accidentally got a large and am a virgin). Does any one have any tips and tricks they used when starting with a cup? Or do I just need the regular/small size? I need to use it because I’m a swimmer and I really don’t want to use tampons because they are sooo wasteful! Please share any advice you have! (Using a saalt cup if that matters at all)