Pretty fun game idea! I learned pretty recently that some planes used to refuel like this so it's cool to play that!
I think a good general tip is to always show the tutorial/how to play before the player starts for the first time. I skipped the "how to play" and didn't realize I needed to use the mouse so that was confusing.
It also doesn't seem like there's any real incentive to try and avoid the obstacles. I guess the score is lowered at the end, but it might be more fun if hitting an obstacle while refueling meant fuel decreased (because it leaks out), so you had to stop refueling if you thought you were about to hit something. Would make it a fun strategy.
Congrats on finishing your game!