I used it to cover an old live edge clock I had sanded down (after removing the
digits) but it left a couple rough spots. I'm going to mount a couple euro's on it. My question is, if make some more, can I just
pour it over the rough spots or will I need to cover the whole thing again? Anyone have
any experience with this?

Most resins will stick to themselves, but not all. I would test the resin by covering a small board, letting it dry/cure and then pour some more on top and see if it dries and sticks good.

I went ahead and poured on the bare spots but it's not at all even. I'm gonna try and sand it down even. If that doesn't work, I'll sand it all off and try again.

Looks great