Coyote Foxtrot

There are Mun craters, and then Mun large craters.

Using RCS thrusters will typically cause a change in orbit and relative velocity to your target as the thrust is not perfectly only effecting orientation causing some thrust to change your orbit. This issue is exacerbated with your craft here as RCS thruster are not placed symmetrically around the CoM of the orbital maneuvering portion. This will cause the RCS thrusters fire in an uneven matter and although it can rotate your craft, it has unwanted thrust changing the orbit.
One method is to have your new station module isolated and maneuver itself with its own RCS thruster system. Of course, this will add complexity with needing command modules and whatnot added to your module.
Another method is to toggle off the RCS and rely only on reaction wheels to rotate your craft. It is a a slower unless you have large or many of them, but they allow you to orient yourself without having thrust which can change your orbit (and relative velocity to your target). You currently seem only the small integrated reaction wheels that come with the command module you are using. You could stick with that and slowly rotate with RCS off or add additional reaction wheels near the CoM to allow for greater rotational control.
A note about your module is that it seems to primarily be batteries with no way to generate electricity. It's easier to think of KSP's electrical system as power production and capacitors. The batteries can be thought as the capacitors and store electric charge for those moments when you need a lot of electric charge quickly (e.g. running/transmitting science experiments). Unless you have things that need electric charge production to match their usage, you can simply used a limited amount of them whether it be radioisotope thermoelectric generators (RTGs), solar panels, or fuel cells.