Visual attitude
I fly a C42, and when learning, I felt just like you regarding slow/fast and high/low. My instructor suggested I use the vertical bar that goes between the bottom of the windshield and the top as a simple attitude reference. Ask your instructor to set up your approach, and look to see where the horizon lines up on the bar – then see where the horizon is on the bar with one stage of flap, and also with two stages of flap. Mark the bar with a bit of tape/different coloured sticker for each part of the approach. If you use these reference points, and you are aiming at your touchdown point on the runway, then your speeds will be spot on - my instructor covered up the air speed indicator and just told me to use the visual attitude and increase/reduce engine power as needed (ie horizon to my marker on the vertical bar) and the speeds were always spot on.
Today, I know these attitudes without needing to look at the markings on the bar, but it did help when learning!
As you’ve probably noticed, the C42 can lose airspeed very quickly if you have full flap and low revs, so keeping the correct attitude in approach is so important, as is keeping the speed down within the white arc with the first stage of flap!
It will come!