Okay, how much danger am I in? I used a Mr Beer kit...and bottling added priming sugar. Unfortunately I got on the wrong line - having 500ML bottles, I added the priming sugar for 1 liter bottles. 2 and 1/2 teaspoons and it called for only 1 teaspoon.
You could end up with bottle bombs, and even if you are lucky, when opening bottle with much more pressure, you risk gushing.
I would empty all bottles in a fermenter, leave it to ferment dry and bottle again with the right quantity of priming sugar. I prefer to prime the whole batch in a bottling bucket, then mix it well. When you prime the whole batch, you do not have to care about bottle sizes.