Oh big time bummer! Looks like it won't be too hard to rip out, just time consuming. I once pebbled a 12 inch block on a quilt, then decided it looked bad. You talk about some time consuming ripping. :P

I always use a sandwich to practice with, also after cuting every 4th stich use an eraser to pull out threads

It looks like it might be easier than most ripping - the tension should make it easier to get under the thread.

been, there, done that. sorrryyyy.