I'd suggest a thicker piece of paper. It's quite a common problem and is referred to all over the forum as "The Paper Shim Trick". I've read some people taking theirs apart and resetting the chip in the case to fix it, but this is kind of an At Your Own Risk sort of thing.
Like I said, I'd suggest getting a nice good wedge of paper down in there, hopefully you have a top loader card so you don't have to take the card out. If you have a side loader, some people have suggested using pieces of black tape on the back until secure contact is made.
Good Luck, unless you got it from an easy place to return it's not usually worth sending it back, especially if you had to import it, just keep trying tricks till you get it stable.
Take care,
Zrynn