It will be about 1% ABV higher, not a problem for most styles. You can dilute it now or in the bottling bucket, just boil the water first and cool it. Or bottle as-is.
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Relax - I'd say if you really want to water it down & try to hit the right % for ABV, just do it like David recommended above & add more water when you go to the bottling bucket. Instead of disolving your sugar at the recommended amount of water - go bigger on the water ( up to 1 gallon) and then you can dilute the beer while you're racking from the fermenter.
You won't hurt anything by opening up the bucket, but it goes against the general Relax, don't worry routine. Let the yeast work in peace.