Multisite should be by subdomain, instead by subdirectory

Hey all,

I just converted to multisite—again. I did this a few weeks ago, with disastrous results, and thought I'd successfully reversed it. Looks like maybe not?

Previously, I'd set up a wildcard domain in my cPanel, and thought it was ready to go. When converting this time I wasn't given the choice between subdomains and subdirectories, and it's clearly now by subdirectory.

How can I undo this multisite installation (thoroughly) and start over?