Question

I'm on my second cycle, second cycle trying my menstrual cup. Both times it was good on my lighter days , felt like a miracle, BUT as soon as I hit my heavy days it started leaking and I was so sure I put it in correctly. I'm almost going back to tampons. It was working so well on my lighter days too, but as soon as it turned heavy it started leaking and I don't even think the cup was filling up. Is it just not working for me???? Any tips? Did this ever happen to anyone?!