One last thing to consider with your rotary cutter - make sure you have only one blade loaded in it! When you buy blades, they have an oil between them and can stick together. It's not very obvious to the eye when you load the blade, but it has a negative effect when cutting fabric. Sometimes it will look like you have two cuts (very close together)and sometimes it seems the cutter skipped part of the fabric - and that can happen with the same cut on fabric.
Good luck!