How do i make my plane go further?

I am making a balsa wood plane design rubber powered (squirrel design) and am wondering how to increase flight time it is in the air.
and increase lift but sustaining hight in the air

Can you curve the trailing edge of the wings down a bit? This may increase the camber of the wing and give it some extra lift and keep it aloft a teeny bit longer. You might try it. If it causes too much drag, bend it back up a bit.

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