Find a place up front and be prepared to take notes like you are already enrolled in the class.

If the professor calls roll, they might ask if anyone’s name was not called. If they ask why you aren’t on the roll tell them you need to add this class. Most will want to take care of this business after class, so be patient.

Be prepared, however, not all professors will add students over the limit. Even if the school will allow this, it is still up the professor’s discretion.

I got into a full class simply by asking the professor at the end of class. She added a couple of people who were not enrolled.

Good luck.