A few years ago I tried multiple times to make a screen for my kid’s bedroom and failed each time in a different way. I got so angry I gave up. Each time something doesn’t line up or fit correctly even after checking the dimensions multiple times on each try.
Seemed like different problems each time, but mostly that there would be a gap in the window or it wouldn’t fit, or the frame would warp after installing the screen in the frame.
What material are you using for the frame? Wood? Aluminum?
Aluminum.
For the warping, I find that I have to brace the screen frame, unless it’s a small window.