I know you said not to get angry, but why on earth would you perform something that you can't play completely?

There is no respite from the constant pulsating of the alla marcia section without the slow bit, very important. If you performed this for an educated audience I am afraid you would be crucified.
People cut bars out of pieces often but it has to done in an educated and musical way. If you were my student I would never have let you perform a piece with that big a chunk taken out and, in particular, taking out something which reduces this musical satisfaction of the piece.
As for constructive tips I would echo some of the thoughts of others:
1/ Work on the voicing of the chords, play the melody on its own. I would recommend singing the melody to yourself while playing it on its own and then playing it with the chords so you can hear it.
2/ Don't play the piece at a speed that you can't handle and start shanking the chords. This piece is very chord heavy and thick textured, when you start missing chords because you can't make them it starts to sound hollow and quite obvious, work on these slowly. I think some of it may have to do with playing your chords with a stiff wrist and 'parking' the notes on the chords rather than playing 'them'. Sorry this is really hard to describe in words and difficult to explain without seeing you play.
Good luck, keep plugging away at it.....
DMK