For the original jelly roll "race" quilt it is really essential that all the strips be the same width, whatever that width is, because of the way they're pieced together, end to end. If you intend instead to sew one strip completely (along its length) to the next strip and repeat this process over and over, then it won't matter what width the strips are. In fact it will probably add interest to the design if they're different widths. However your quilt will wind up at about 42" (the length of each strip) x 80" (40 strips sewn together), so you will want to think about adding borders or doing something else to change the proportions.
I wouldn't wash a jelly roll, or any other precuts, because the strips are sure to fray. If they're not well sized before the washing, it will be much worse after you wash. If the strips are so poorly cut I would probably take them back to the shop and ask for a different product or a refund.