That can happen! Here's a few tricks:
1. Eakin Seal will protect that delicate skin right around your stoma. I use the whole ring and even make it smaller than the opening so it is up close. The mouldables are great, but they may not have enough "support" to go 6 days for you...try changing at 4 until the skin is cleared up.
2. When you say you left the are "open" does that mean that the wafer doesn't go all the way to your stoma? If it is not right up to the stoma, that area will continue to be irritated.
3. Since you have a colostomy, you could probably get away with only using an ES when you have irritation...I think you mentioned something about irrigation on one of your posts...right?
4. When removing your wafer, hold the wafer and push your skin away...don't try to pull the wafer away since that will only breakdown the skin.