Wow, thanks for all the replies! I have learned from all of you. Yes I think that I used my ruler and mat interchangeably and there's the answer to the blocks being off. I do use my ruler to measure but I also used the mat not knowing any better. I have been learning quilting on my own but thanks to all of you I will be turning over my Olfa mat and use the line only for alignment and stick to using my trusty rulers to measure! Also I wasn't thinking about reimbursement of the tweaked mat (not an Olfa) but just thought they should know but after reading all your comments it sounds like most people knows mats could be off so they use the mats for cutting and alignment! Well this has been a good lesson and now I think my cuts will be more uniform. Thanks everyone! This board and your responses are my teachers!