Hi @arami364 ...
The first thing to check in Canvas is to click on "Courses" >> "All Courses". On the "All Courses" screen in Canvas, do you see your courses listed there? If the courses are listed there, they may not be published (look at the far right column). If a course is not published, then it means your instructor has not yet given you and your classmates access to the course yet. The instructor needs to publish the course in order for all of you to get access. However, if you do not see your courses listed on the "All Courses" screen, then you will need to reach out to your school's Online Learning / eLearning / Distance Education department. They should be able to help you with your enrollments or point you to someone at your school who can assist with this. I took a few minutes to browse the University of California, Riverside's website, and I found this page which seems to have some troubleshooting/contact information, and hopefully it will be of help to you:
Welcome to Your New Website! | Elearn (ucr.edu)
Keep us posted here in the Community ... thanks!