Two comments really, which your instructor might already have made:
1) Good approaches lead to good landings. If you're not stable in the approach by 400 ft then you're going to be struggling to make a good landing. By stable I mean on the centreline with any necessary crab angle to correct for crosswind, flaps at the landing setting, speed trimmed for the approach and making only minor adjustments to power to maintain the glideslope as the wind changes. If you're still messing about at 200 ft while the speed drops through 60kts and the runway is sliding off to one side, you might as well start the go-around then. Many airlines have a rule that if an approach is not stable by 500 ft (I think that's the right level) then they must go around. If it's good enough for them then it should be good enough for you.
2) Beware of ground rush. You mention you are OK at 100 ft then it all goes to pieces. Just remember that if you have flown an approach from 1000 ft reasonably well to 100 ft using the techniques you have been taught then why should those techniques not work for the last 100 ft? The ground rushing at you tends to throw most people because it suddenly dawns on them that the soft medium is suddenly about to meet the hard one. They tend to forget all about maintaining the crab angle and controlling the flare.
It seems to me you've now got a bit of a complex that you can't land the aircraft. You need to get this out of your head and relax. Have you tried going for very low approaches and go-arounds (5-10 feet) and flying along the runway without actually touching down? This should get you used to the roundout and flare and correcting for crosswind without worring about a boneshaking touchdown.
Just a few ideas. Keep at it, you will get it cracked. I bet your instructor has made a dodgy landing with you on board. It happens to all of us sometimes!
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"Take-off is optional, Landing is mandatory"