i called the store i bought the battery at, explained my situation, and they said as long as i have the packaging and hadnt used the batteries i could exchange them for another size.

the plane weighed in at 4.6oz (130g) and the recommended flying weight is 120g-140g, so i dont know what a larger battery will do. maybe the park 300 is a bit large for the plane, but maybe i can make up with it by having the larger battery?