Here's the thing . . . it's either going to come off as two ways . . .
1) That you really are just saying the show was off-Broadway, that is not a Broadway show. (what Libby said)
2) That you are try to pass an off-off-broadway, or off-off-off-in someone's living room as an off-Broadway show.
I guess it really depends on what you are applying for. If you are applying for work in NYC, then the producer probably already knows what contract the show was, based on what theatre it was at, etc, etc. It's a little bit of a crap of shoot really. I like the way Libby breaks up her resume, it makes perfect sense, when you have the Broadway credits, then it's saying Broadyway, Off-Broadway, Regional, Touring - I get the sense of where the work falls, but let's play the example where there is no Broadway credits, and you have just Off-Broadway, and then some other categories - like educational, regional, etc. Then the Off-Broadway classification may look like you are stretching your resume beyond your current skill level.
But, this is such a style and splitting hairs discussion, go with what looks good on your resume and sells you the best. Given that you just got your card, people will probably be able to tell form your resume what contract and what level your shows have been produced by.