Main Sheet Problem

Hope you all had a Happy Thanksgiving! I'm a new Sunfish sailor and have been having a problem with the main sheet being caught on the corner of the transom after I tack. I suspect I've had too much slack out on main sheet. Today while tacking I pulled in on the sheet as I was heading into the wind on the tack. This seemed to work with some success but I still was getting the main sheet caught on occasion. Can anyone please give me some advice to avoid this from happening. Thanks!