Perhaps from your post you are being taught just the forward slip, this is fine and best to learn first. Else it is really hard to apply it at the end of a crab. It sounds like you are looking for a magic control input to sort the problem. Not going to happen, all the way down the amount of input keeps changing as the wind is not constant. Just cancel the drift with bank, keep it straight with rudder and carry a few knots for the position error and inefficient flight mode. Remember don't remove the inputs when you touch down, it's likely you may need to end the landing running with full aileron into wind and whatever rudder to keep going straight.
I would also check where you are looking during the landing flare. All landings are harder if you don't look well out from the plane, crosswind are just worse still if you look too close in.
Remember, whichever 'method' you are being taught it is training, in the end most people use both crab and wing down combined. Personally I found it much easier to learn crosswind landing using the wing down technique throughout the approach than the crab and kick it straight method which during training never came out too good. Partly because I was rubbish at judging when to kick it straight, partly because I didn't have the confidence to transition to wing down quickly enough to stop any drift before touch down.
Main thing, enjoy, it gets easier in time.
PS remember if doing a forward slip the 'picture' out of the cockpit is a bit odd, if it isn't clicking ask your instructor to demonstrate a couple of landings and just fix on the picture that day, it will help you pull off a couple of reasonable crosswind landings and help with the confidence.