The cabin air filter should only fit in one way, unless you forced the shit outta it, and if that's the case, you'd probably know it wasn't right. So, if it went in without much trouble, its probably correct. That being said, on the outer edges, there are small tabs that fit into a recess in the "tracks" that it slides on. They will match up. Again, check the tracks on the two sides that the filter sits on, you'll see what I mean.