Hi Kiki! Welcome to the Quilt Board!
The whole don't wash or prewash is simply a personal preference, and you'll hear lot's of pro's & con's. The nice thing is it's your quilt, you can do it however you want, no quilt police here! That being said, since it's going on the wall you shouldn't have to worry about shrinkage, I don't think you have to prewash.