Cabinet Difficulties

Since I now have sizeable hole in the bathroom wall right at eye level, I though I'd try to fill it. I'll still have to paint before I install a new cabinet, but it's nice to have a look.

Before she left, H and I picked up a medicine cabinet, vanity, sink, and faucet to put into the bathroom. Tonight I cracked it open. I had some difficulty sizing the medicine cabinet when we bought it, because it was tough to tell what the actual width, height, and depth of the pocket were that I'd have to fit into. The trim around all four sides threw me off - it's tough to know what its covering. Now that the old cabinet it out, it is trivial to measure.

As it turns out, the cabinet we purchased is a non-starter. I'm not sure it's really meant to be set into a wall - the trim is wrong for that. Plus, the dimensions are wrong by an inch or two all around. The dimensions of the cabinet don't even match the dimensions on the box. Compare 30W x 29-1/2H x 5-1/2D that's on the box to the 28-7/8W x 28-1/2H x 4-1/2D the thing actually measures (minus the trim).

But, we're going to need that hole filled, somehow. I'll take the cabinet back and see if there's something similar in a different size. If that fails, well, I'm kinda handy with a table saw...