Having a gun fitted is not all that expensive BUT, before it is really worthwhile you need to have a consistent gun mount. Best way to do that is to shoot a lot. The human brain can adjust to a lot of things, including less than perfect gun fit. Your eye will send a sight picture to the brain, and the brain learns what sight picture results in a hit. That's how Tom Knapp can hit a duck flying shooting behind his back no less.
I have owned a lot of shotguns. I bought an adjustable stock quite a few years ago on a whim, and when I got thru adjusting I was so close to standard factory dimensions I decided maybe I was so ingrained it was a waste. When I look at a gun, I mount it while focusing hard on an object, and then try to quickly look and see where the gun is actually pointed. As long as I am close I have no big issues. This may not work for everyone, and it is not perfect. The drawback to having a gun fitted is that if you later decide to sell it you need to find your twin to sell it to, or take a hit on the value. So you need to make sure that is a gun you really intend to keep first.