My catapult is really weak

Hello everyone, I was making a catapult for the new season Level Up. When it launches, it does not go very far (a foot at most). It is not that the object that I’m launching is heavy, because it is a little bit lighter than the official bean bag. I was wondering if it was the winch or the rubber bands. When it releases the arm, the winch creates a little bit of friction. Also, I have a tensioner, which limits the amount of rubber bands. Also, even if I remove the tensioner, adding too many rubber bands makes the back of the robot bend. Please let me know if I can fix this issue without removing the tensioner, or if I need to sacrifice the tensioner. Note that I am not that experienced, and this is my very first time building a catapult, so any general tips about building a catapult will be very much appreciated. I also only have the education kit so some materials are limited.

Here are some pictures:

I don’t see a hard stop, maybe you could try and place something to stop the catapult at a 45 degree angle? And yeah you probably need more cross bracing than just standoffs. They work, but having actual beams running through is probably a better choice.