Thanks everyone for your reply's. Bottled last Sunday so I suppose I could open them up to drop another oner in, but I think I will just see how it turns out. Might take Svyturys and Rudi101 advice and see what happens.
Can somebody tell me what happens when only one carb drop is put into a 750 ml bottle. It should have been two but I stuffed up. I suppose I will have a low carb beer. Should it taste ok. I used a Morgans dark ale with a malt extract.