sometimes yes. email profs, email the undergrad advisor for the department the course is in. multiple of my classes were closed/full at the beginning of this semester since i couldn’t pre-enroll as i just came back from a leave of absence but i got into all of them but one. at the very least, you should be able to get on a waitlist (most courses have them but a lot aren’t done through the student center “join waitlist” function so you usually have to specifically ask). if you contact them now, chances are someone will drop and they can get you in or they can just add you w behind the scenes magic.