Am i looking at it the wrong way? but did you put the decal on the TOP side of the ramp?
I would stick it underneath the ramp, to protect it from ball-wear.

Also, if it is stuck on the underside, you can cut the 3M tape a bit wider, so the side edges align at the edges of the ramp to help conceal the decal-edge.

Hopefully you scanned the decal into your PC for future use, since you can't get them ;-)

my 2c ;-)
MM