this cub doesnt slow down,
First, make sure it isn't nose heavy - then make sure you have the idle set low enough. If it won't idle very slow, you need to lean the low end mixture.
After all that, if it still doesn't like to come down, put a 14x4 prop on there. It will give more thrust, fly it at a scale speed, and give more drag at idle, which means steeper approaches.