UC’s take Junior level transfers so 60 semester/ 90 quarter units by Spring prior to matriculation. HS grades and test scores are not considered.
If you are a CA resident, then returning to California and attending a CC will help get you to your goal. If you apply now for Fall 2021 as an OOS applicant, you would have the lowest priority for transfer.
What is your current GPA at SMU? Have you checked the transferability of the SMU courses?
The UC transfer admit GPA range was 3.89-4.00 with a 12% admit rate.
I would not rush the transfer process and try to complete all Econ requirements prior to transfer to put yourself in a better position.
UCLA has TAP which gives your priority for transfer and the link below lists CC’s that participate in this program.
https://www.admission.ucla.edu/Prospect/Adm_tr/ADM_CCO/tap.htm
Best of luck.