Sorry, I'm not sure what else might be wrong. I wouldn't think that "cleaning out all the clutter" would make a lot of difference though. Try this: start Garmin MapManager (in the Applications folder). Select catopo11 and click the "reveal in finder" button. Now click on catopo11.gmap in the window that opens in the Finder and choose File > Get Info.
What do you see for Size? I get: 433,609,968 bytes (435.4 MB on disk). If you see something smaller, there must be a problem with your download.