If you fill it too high, you may have yeast mix get into the tank. If you see any cloudiness developing, run, don't walk to dump the mix and do big water changes.
Really, you are better off to just open it up now and take a bit of liquid out of the bottle. You won't lose much stuff. The sugar is mostly on the bottom, the yeast is well mixed in the liquid, the baking soda is probably well mixed too.