I think you'll do great! If you're really nervous try it on another sweatshirt or t-shirt first so that you can work out any kinks that might arise. You're not alone in that fear of trying something new. When I am trying a new design of anything I make the first out of fabric I don't care about.
At least with your sweatshirt you just have to pull the seams apart at first and there is no cutting. If you panic you could just sew it right back up. post when you finish! I'd love to see how it turned out!