I wouldn't worry too much about cadence now. Spin at a rate that feels natural to you.

Concentrate more on you pedalling technique. Try to even out your power through one full rotation. You shouldn't be bouncing up and down in your seat just to maintain a high cadence. Or mash the gears.

ONe quick way to know if you are mashing or not is have some one look at your upper body. If your upper body "pumps" up/down with each down stroke then you're probably mashing. If your body pumps down toward your left when your left pedal is on the down stroke (same on the right side) then you're probably mashing. Your upper body will be fairly "quiet" if you have a clean pedalling action. power into the cranks at the top-down-bottom-up stroke. Once you learn to do this without thinking about it, your endourance, and speed will improve significantly.

just ride a lot and enjoy your ride.
Shawn