I can't stress enough the need to UNDERSTAND what you're working on. Just viewing a tutorial isn't necessarily enough. To make the one point that might help set you onto the right path. The limit screws are line the concrete barriers along the length of the bridge. They define the width of the roadway, and prevent you from driving off and into the drink. But they don't affect your actual lane placement, you do that.

Likewise with the derailleur. The limits are just that the limits, but the position of the derailleur with each shift is controlled by you via the cable.

Watch or read a few tutorials until you have a good sense of what to do, or visit the co-op where the hands-on guidance is a much better learning environment.

Or, spend dough that you don't need to.