No. 10 1/2 is smaler than 10 3/4 you need to add 1/4. The next question is will the wider sashing look right with your blocks, or just leave the shashing the same if your finished quilt is say 5 blocks wide your are only loosing 1 1/2 inches in width at this time, will this affect your overall quilt? Personally if it was me I'd leave it alone unless this is a compation quilt.