Well I'm back in business, although I didn't really use this method.
I used the recovery mode and then deleted the Xastir folder I had
created. I sure didn't expect this partition to fill up so fast, I'll
have to see if it's as big as I wanted --

Hmm -- maybe I'm not recognizing the file structure. When I create a
directory, should I do it on my desktop? It appears the place where I
created it only has 346.4 mb, and 346.2 were already in use -- that's
/dev/disk

Conversely, my home directory shows to have nothing available at all.