Hey man,
You may have figured this out by now, but here is how you could do it.
Square frame out of 2x4 or 2x6. Around the inside, install punched angle iron (same stuff that holds your garage door opener to the ceiling, you can get it in lengths from any home store) the entire way around. This is where you will mount your impact screen with bungees.
If you get an impact screen with velcro flaps, you can then attach those somewhere, and install impact panels to hide the seems. That will give you a professional built in look.
You can mount the frame however you want to the drywall, but it's mandatory you give at absolutely minimum 10" from screen to wall. And even that is tight depending on how taught your screen is. Be aware, if your screen is too tight, you risk bounce back, if your screen is too loose and close to the wall, you will pinch the screen and risk holes. 15" is a good distance. Keep your ball speed in mind here.
If you build the frame and provide any sim screen manufacturer the measurements, they'll get you the correct size to fit inside the frame properly.
Happy to jump on the phone and walk you through if you'd like.