Well, you run the risk of it shrinking enough so it won't fit. Of course, that could happen when you wash it after you sew it too. On the whole, though there is no really good solution for this problem, you might be best off washing it before sewing, though that gives the problem of fraying in the wash which can reduce the amount of usable fabric. You might want to stitch as close to the edges of the cut pieces as you can, to reduce fraying. Or sew it, and then always wash in cold and never dry it in the dryer for more than a few minutes, only enough to get it started drying. I don't like the second solution as well. I don't know what you're sewing but if any of the fabric is cut on the bias it could shrink after sewing and make wrinkles or sags that can't be ironed out.

Next time you buy fabric, follow my rule. All new fabric goes straight into the laundry basket. It does not appear, even for a moment, in the sewing room until it's been washed and dried.

100% cotton fabric is likely to shrink when you wash it (and probably wrinkle too). If you wash it by machine now, I agree with Karen that you're going to get a lot of fraying and you will have to reduce your seam allowance. You could try hand washing it.

I think the best solution is to go ahead and make your skirt, and then just make sure you ALWAYS wash by hand after it's been sewn. If you forget and machine wash it, it will probably shrink and you won't be able to wear it anymore.

I have 100% cotton fabric that is suppose to be washed in warm water. However, I already cut it because I completely forgot about the pre-washing step. Is it okay if I don't pre-wash the fabric at all before actually sewing it? Or should I wash it even though I cut the pattern already? Please share your advice

Thank you so so much ?

P.S. sorry if this question is in the wrong category, I couldn't find one for sewing