wp-cal usage

I installed the calendar plugin wp-cal, which from what others are saying here and elsewhere is a good calendar plugin, but when I followed the directions, I didn’t get it to work. the plugin is installed, I edited the file cal.js according to the directions, and I created a page with the line:
<!--cal-->
in it. The options panel shows up just the way it is supposed to, but I don’t have a calendar. What am I missing?

Thanks,
Thomas
https://www.buffalobiketaxi.com/home/calendar/