HELP! MAJOR LEACKAGE!?

Okay so today is my third day trying tampons. My flow got a little heavier than it was when I started. I put in a tompon and had it in fine for two hours. I felt wetness so I went to the bathroom and when I checked, it was really leaking badly. When I took it out, it wasn't opened like it should have been. I switched back to pads for the time being. What am I doing wrong! I'm sure I had it in right because it went in fine and I couldn't feel it at all.