My thoughts: Press your seams in opposite directions so they 'lock' together. Oh and do make sure you pin the whole seam if you're a beginner like me. I saw in the Winding Ways book that you should only take small 'bites' of the fabric when you pin your seams together - I have been trying to do that since reading that book and I think it helps. Other than that, all I can suggest is to keep going. The more pinwheels you make, the better you'll get at it and the closer you will be to having a finished quilt for your great-grandaughter. I'm sure she'll love it even with a couple of less than perfect centres.