Log out of Pega Academy - don't just close the browser window, click on your name in the upper right corner and select Log off.
Then, just to be safe, clear any cookies from academy.pega.com and any cookies from paexNN-XXX.pegacloud.com The NN is a two-digit number and XXX could be either eu or use. These are cookies from the online exercise environment. Or, you can clear all browser cookies - yoru choice.
Then, log back into Pega Academt and go back to your course.