With my instructor in the plane I tend to come in too low. I'm aiming for the begining of the threshold, trying to make it the 'perfect' landing. Then comes the sink, and I have to add too much power to get back on the glide slope. Due to the extra power I tend to be too high, too fast, and have to hold off for too long and end up bouncing. (I've gotten better tho).
Without the instructor, I have always had near perfect landings.
Relax, don't try too hard. You're in a plane, it's awesome. Remember what you've been taught, anticipate sinks where you'd expect it, come in too high add flaps or go-around. Come in too low and it takes alot more effort to sort yourself out.
But most importantly, don't give up!