2+1 fin sizes on a 8' minimal

I have a nice southern swell 8' epoxy board. it came with 2+1 fins, the center being 8"
now being a beginner, i have trouble judging depth. i am paranoid about grounding my fin and ripping out my finbox or worse. I surf bournemouth/boscombe.
would i notice any difference if i bought a 6" center fin, or can i change it to a 3 fin thruster with an adapter? i previously had cortex 8' and that had 3 fin thruster set up, but there was a manufacturing fault and the fcs plugs pulled out by the waves, not through grounding, but it has made me cautious and worry about a weak point.
trying to take out a bit of the fear factor of breaking my board so i can concentrate on my ride.
now being a beginner, i have trouble judging depth. i am paranoid about grounding my fin and ripping out my finbox or worse. I surf bournemouth/boscombe.
would i notice any difference if i bought a 6" center fin, or can i change it to a 3 fin thruster with an adapter? i previously had cortex 8' and that had 3 fin thruster set up, but there was a manufacturing fault and the fcs plugs pulled out by the waves, not through grounding, but it has made me cautious and worry about a weak point.
trying to take out a bit of the fear factor of breaking my board so i can concentrate on my ride.