I've been doing quite a bit of reading into vivs for my corn and everywhere I looked gave me a different answer. He's only a junior at the moment and in the tank that the pet shop recommended.
I however bought a 30"x15"x15" viv from eBay this evening as for £30 with lights I thought it was a bargain, not to mention a mile away from home! I've read that he should be kept somewhere small for the time being and elsewhere said he'd be fine providing there are plenty of hides for him to use.
How big/old is your snake? A large space for a small corn can sometimes freak them out a bit but if you fill it with decorations and hides etc then it may be ok.
i'd personally go for the 'plenty of hiding places' school of thought. Fake foliage is really good for hiding in and exploring, plus it fills the empty spaces in the viv and looks good to boot :)
If you do put him/her in the viv then make sure you block every hole and also where the glass overlaps as they are great escape artists and will get out of the smallest gaps (even inbetween the glass).
I've also got a March hatchling and I wouldn't put her into her viv just yet even though I also got a bargain so had to buy one sooner than necessary!!
The thing that would worry me (the most) is her getting out between the glass at the front.
Dunelm Mill is fantastic for cheap fake ivy, and PLEASE as others have warned, the gap in glass is easy to get through, there are pics on here of bigger snakes almost getting through before getting caught