Did I make a mistake? Bought Flux 2650 instead of 2200

[nativepaul]

No, it wont stop it from going too many RPM only keeping it at partial throttle or using lower voltage will do that.

Personally I wouldn't put it in anything bigger than an 1:8 buggy or 1:10 sct, but if it is only a spare for a bigger flux, it will likely never get used, and if it does it only needs to hold up for a few months while you get the other one repaired.

Do you have 1 6s pack or 2x 3 s packs? if you have 2x 3s you could wire them in parallel instead of series to use the 2650 safely instead of gearing down, saving a few bucks and you wouldn't have to worry about it going too many RPM.