if you mean the bondo brand auto resin, I know what you mean. Ive made several handles out of jeans and or the cotton duck from walmart and the bondo resin.
sometime in the last couple years, the package of resin changed colors, they also changed the resin. ths new stuff doesnt stinck as much for near as long as the old stuff, and the handles dont come out as shiny or as tough
the old stuff didnt really look good to me anyways until 1000 grit or so. this stuff does end up looking ok, but will never get as shiny as the old stuff. I would try a different brand of auto resin. I know walmart only has one brand, but they sell 2 different brands at home depot {is cheaper there also}, and should carry it at auto parts stores
I still have one can of the new bondo, so will use it up before I get another brand, so wont be able to let you know how that one works for a few months, if you get good results out of another brand please let me know which one iit was.