Q: Magic Mouse

Honestly the only thing you really CAN do is to just use it for a while and get used to it. I know that's not much help but since you don't want to dish out more money for another mouse (which is understandable), all you can do here is get used to the way it feels.

You are using El Capitan.  Although some mice will function with it, many will not.  The magic mouse 2, if that is what you have, was designed to work with El Capitan.   That is what you should work with.

If you have a formal Apple Store near you, take it in and ask them to show you how to set it up, but study this document first.

Set up your Apple wireless devices - Apple Support