If you have ordered the fabric from Fabric Flair please be advised that the cut for the 28ct is 45 x 17
The stitched count size works out to be 12.21 x 39.80
Shops usually add 3 inches some only 2 inches extra on each side.
So Fabric Flair has added 2.40 inches extra on the width and 2.6 on the length for each side. You should be fine if you measure down to start and find the center, some people do prefer more extra fabric and some are all set with 2 inches, so Fabric Flair is in the middle of the road with these cuts.
Since this is such a long project it would be advisable to finish the edges so they do not fray to much as time goes on.