To improve the use of abrasive sheets I suggest cutting the sheet in the following manor.
1) Cut a disk with a diameter that covers your form tool plus enough to clamp on.
2) Cut triangular slits (maybe 5 - 8) out of the disk. The slits should be oriented with the apex near the center of the disk and the base (shortest side) of the triangle on the circumference of the disk. Size the slits to get maximum coverage of the form, without any overlap.

The finished abrasive disk will look similar to a daisy flower (with petals) and should improve your metal removal.

Besides the flower petal approach, I suggest using an abrasive sheet with Pressure Sensitive Adhesive (PSA) on the back and eliminate the hose clamp altogether.
"3M Stikit" (or equivalent) disks w/ silicon carbide abrasive are easily available on-line in a full range of grit grades.