For fixing it, sand the pebbles with a small piece of very fine wet or dry sandpaper- maybe 1000 grit. Then recoat. Much as I love Testors Glosscoat, spraying from cans can be tricky. Make sure the sprayhead works smoothly so you can make very quick blasts when you need to.
I do find it amazing how self-leveling it is. Consequently, I tend to err on too thick a coat rather than to thin.
Another possibility is to clean up the dull area where you sanded by rubbing on future with a clean, soft rag. Build up the layer of future till you get a gloss.