Menstrual cup

Does anyone have any advice on using a menstrual cup. I’d heard they’re tricky to get used to but my first day using it was absolutely fine. Inserted when I first started, took it out and reinsterted before I went on a night out and then took it out in the morning and zero leakage. But today I’ve reinserted 4 times and leaked every time. I don’t feel like I’m doing it any differently and I always check that it’s fully open so I don’t know what it is. It’s my heavy day but the cup isn’t completely full when I take it out. So I don’t know if it’s just emptying it more?