A knowledge base article about I enrolled in 2-Step, but the CAS (or CalNet) login screen still says that I need to enroll. provided by the UC Berkeley IT Service Hub - Knowledge Portal
Sometimes the CAS login screen (what we think of as the CalNet screen) takes a day to get the message that you have enrolled in 2-Step. Check again tomorrow, and you will see that the CAS screen has reverted back to the normal screen.
More information can be found in the 2-Step FAQ page
You may also want to try clearing your cache. Instructions on how to do so can be found on the Google Account Help page