My college (CSUF) requires 120 units to graduate. However, the required classes on my TDA shows 48 units of GE classes and 51 units for my major. That is not 120 units in total. So, my question is, can I take any classes I want outside of those required classes to fill up the 120 units required for graduation? Thanks.
Yes, if the courses specified by various requirements (major and GE) add up to less than 120 units (99 units in your case), then the remainder (21 units in your case) can be any courses you want.
Just be careful that you do not overlook any specific course requirements when planning your schedules. Both CSUFs (Fullerton and Fresno) should have online degree audit or degree progress web sites that you can use to check fulfillment of various requireents.