It might just be your seam allowance is off. Flip your block over and measure the pieces....are they all the same? Does the sum of the pieces equal your desired 10.5 size block? If they do then it's seam allowances...if not then it was a cutting goof. If it's your seam allowance, take them apart and try again AFTER you have tested your accuracy sewing a scan 1/4" seam allowance. If it was a cutting goof, trim all the pieces so that they will come out to the "smallest" size. To help you out, I'm going to attach a couple of PDF files. One will have templates the size you need for the 10.5 and one for a 9.5 block. You will have to tape a couple of pages together. Also set your Page Scaling to NONE when the print box comes up.
I know that taking it apart will cause you a lot more work, but you will be so happy with it in the end.
Edited to add: Someone posted the link to this blog (can't remember if it was on this forum or another), she has great instructions, with pictures on how to get the scant 1/4" seam.
http://quiltingisstillmypassion.blog...e-part-ii.html
Hope this helps.....