How many hours do you have now? I'm guessing not too many and I think what you're seeing is the inconsistency that we all went through as very low time pilots. It sounds like you just need to fly more, and get some successes under your belt; the consistency will arrive as you start doing things right more often. Have a look at the next thread re full-stall landings etc. Correct approach speed is vital, as is having a "make it happen" attitude. Never let the aircraft touch down until it's in the right attitude (which your instructor can demonstrate on climb-out or at altitude, when there are fewer things happening), properly aligned with the centre line etc. You're not there as a passenger so gently but firmly set yourself up - don't feel like it's all happening around you.
By the way, has your instructor tried the old trick of making you fly level above the runway without touching down? Of course, as a low-time pilot you won't manage to keep the aircraft off the runway, but you'll learn good touch-down attitudes. Worked for me
