It wont slip through, you're too determined to let it go man.
3200 ft is awesome. You can do alot with that amount of space with the triangular grid system. And for it being a first year haunt, better to make it smaller and awesome, than possibly too large and not as detailed. Plus weren't you worried about it being "late" to start?
I've read from numerous places that a first year haunt can be awesome even with only 2400 ft. If it comes to it, starting small may end up being a great thing you were forced into. A committed mind can use the positives of any situation to make something good happen!