When we quilt we learn some things simply by experience. And, I think it important to use those experiences as opportunity to make different choices the next time. From my own experiences over many years I would make the following observations. Cotton batting does shrink when washed as does cotton fabric. To minimize this appearance I do not wash either beforehand. Both shrink but it is not as obvious because both shrink at almost the same rate. When you prewash some of the fabric, it is already shrunk when you add the unwashed batting. The batting shrinks and makes the fabric look more crinkly. Contrary to what someone else said, I would wash the unwashed fabric. You can put the border pieces in a lingerie bag to control the strings. If the backing pieces have had the selvedges cut off, wash them on the gentle cycle or simply soak them and dry them flat rather than agitate them in the dryer. If you choose 80/20 batting you will have somewhat less shrinkage. If you use polyester you will have no shrinkage in the batting and some shrinkage of the cotton fabrics unless you wash it first. However, the feel of the quilt and the warmth are greatly affected by the batting. I, over the years, have tried all these combinations. My preference is 80/20 batting and unwashed fabric. I always wash a quilt before gifting or using. I dry them flat on a plastic painters drop cloth. I do use other batting, like silk or wool when I want a special effect-but I wash everything after construction. I wish you well in your quilting journey.