Hi!
Please don't panic. The body will just work out the excess of vitamin C through the kidneys.
Please be aware that vitamin C is not just in peppers; it is their veg mix, in their pellets; fresh growing grass is high in it (which is the reason why piggies never had the need to make their own in the first place since grass and hay is their main food source). Even hay still contains a little. Recovery formula also contains vitamin C.
All you needed was to give two instead of just one tablespoon of pellets for the day but to be honest, your piggy won't fall ill if they do not get much in the way of vitamin C for a short space of time. Real scurvy is generally the result of longer term malnutrition (no hay/grass and rabbit instead of guinea pig pellets).
Please do not supplement regularly with extra vitamin C on top of a good diet. By overdoing it, your piggy's body will simply accustom to the high levels and react ironically with scurvy levels whenever the high level drops, even though it is still well above normal levels. If you are supplementing daily, then you need to lower the dose very gradually in order to not trigger scurvy. A one-off high dose won't hurt. In the case of a real illness it is much more effective to a 2-3 weeks booster course because the body will react to that much more.
Most of the scurvy cases we see on here are actually from those long term overdosing cases. None of us long term owners supplements with vitamin C but none of us has ever had an issue with their piggies suffering from scurvy because they are getting enough vitamin C from a range of different food sources.