Online undergrad

Hey, this will be my first year doing uni and I’m doing it completely online as I’m not in a position to move near campus yet. I’m doing the Bachelor of History and enrolled in my units today and when I went to make my timetable it only gave me the choice to schedule one of my units (a flexible unit) and none of the other 3 I’ve chosen. Is this a glitch? Does it mean classes are full? Or because I’m doing online does it just simply mean I don’t have to attend classes and lectures at a specific time online and will just access them at my own pace? I’m so new to this and a bit stressed and thought I’d ask here first before ringing the uni again because last time I did I was on hold for 2 hours. Thanks!