Everyone is right about the most critical issue with this piece is the perspective. And I can honestly understand the sentiment of not wanting to make such drastic changes to such a large piece, but I highly suggest you try to address the critique anyway. Your piece is still in such a rough state that it's now or never. There's really not a lot of pixels that you've made a final commitment to.
With that said, I think there are ways to address the perspective with minimal amount of rework. The perspective line where the cliff-side meets the water is the primary offender. If you fix that one line, the piece drastically makes much more sense to the eye. The issue here is the cliff is suggesting a higher perspective than what the sea-level depicts:

Currently, it's tip nearly meets with the horizon line which would imply it's as far away as that island you have in the distance. Obviously that's not what's intended.
This can either be fixed by raising the horizon line to meet the suggested perspective of the cliff:

or you can lower the perspective line of the cliff to meet the horizon line:

Just shifting things around in this pretty rough state is fairly painless. There are other contributing factors to the wonky perspective, but this one was the most major. Between the two solutions, I think the rest of your piece supports a much higher perspective angle, so I'd probably go with raising the horizon line.