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What soft synths did you use?

To be honest, I think you need to go back to the planning stage before getting too much into the mixing and mastering required.   The sounds didn't work well together, so I would look for more complimentary sounds first.  The structure of the piece needs more planning, and also the levels varied a lot - not sure if you were adjusting frequencies, or if it was a velocity thing, or if it was the envelope of the sounds, or a combination of those things.