I was doing the same thing with my chopper and I ended up straining my back a bit. Veena was generous enough to meet me in chat once so she could show me on camera something that helps - your shoulder position! They're always hammering it into our heads SHOULDERS BACK AND DOWN!!! and that's why. I practice holding my shoulders back and down when I invert (you should do it all the time but it's better to practice it on the invert instead of the chopper so your legs are there to help catch you) so I can get used to the feeling. I'm still working on it because it feels weird, but I've already noticed that when I try it with the chopper, even though it's far from perfect, that little bit helps take the strain off my back.
If you're finding you're having trouble because the muscles between your shoulder blades aren't quite strong enough, look up Veena's shoulder strength video. The exercise she showed me is similar to the YTI or ITY or whatever it's called, except for one difference. Take the T position - arms straight out to both sides - except hold you're arms slightly further back. This will bring your back into play to hold your arms up instead of just your shoulders. Like I said, look up the video so you can see what I'm talking about.
Also, to help get you more vertical, pull your hips up as close to the pole as possible. Because your inside arm and shoulder are on the opposite side of the pole as your hips and legs, you won't be able to be perfectly straight up and down. So just pull that pole up to as close to your no-nos as you can! 😜
