Help! Brand new disc user

I’ve just been trying to use a Nixit disc for the first time today and I’m really struggling. I think the issue is that I’m not sure if the disc is sitting down low enough at the back, so it doesn’t seem like it wants to tuck in above my pubic bone at the front. I’ve read the comments about putting it in horizontally but I’m finding that difficult to get right because my fingers are underneath when I’m inserting which naturally tilts it upwards. Any advice welcome!