Insufficient storage, adjust your settings: How?

New user doing initial backup and I just got this message: 

Insufficient storage space to backup this computer. Please adjust your settings or Buy More Storage.

 

But there is no link to adjust settings, only to cancel the job.  Do I have to cancel the backup to adjust settings?  Should I let it continue until it's full, or will I get an error and have to start all over? It's currently transferring and is at 8%.

 

I bought 100GB of storage and it calculated that I had enough storage before starting the backup.  Why does it now tell me it's insufficient?