This can be hard to do but try not to think about the event all the time. Tackle each little part of the planning at a time. When you have time, do some relaxation first then try some visualisation. First just imagine getting to the church ok. Make sure you concentrate on it going well. Then move on to getting dressed and ready. Make sure you don't get too anxious as you imagine it. It's kind of like the exposure stuff but just doing it in your head. Also, remember, something always goes a little wrong during a wedding, it's OK. It won't ruin the wedding. People will understand because I'm sure they have had something happen at theirs. My son was ring bearer at my sisters wedding and he passed out. The wedding went on with him sitting on the floor, and my sister is still married 16 years later. Make it your purpose to see it in your mind going well. If you do think of what could go wrong, follow it through, chances are when you get to the end of the "what ifs" it's not going to be all that bad "even if".