It also helps to not sew too many strips together at the same time. Say if you have 24 strips in the set - sew them in groups of3 or 4 and then sew those together. It is almost like rotary cutting in that you need to straighten up every few cuts. It seems when the bow starts it just multiplies.
Pressing vs ironing. Ironing - that is like you would a shirt or blue jeans tends to stretch the fabric. Pressing is just that......gently putting the iron down and moving it over. This doesn't stretch the fabric.