Last I checked you're quite allowed to post your level for the contest ahead of time. I mean, constant testing is approved, nay, encouraged.
The "cannot have seen this level before" rule only applies to levels that were made for purposes other than entry into the latest contest (or entries into prior contests). If the level was being designed as an entry from the get-go, then it won't be disqualified just because you're testing it.
That being said I'd recommend doing it in a private beta or something. Wouldn't want to completely ruin the surprise, right?