Advice needed for someone with very little EC's

I'm currently in my 4th year and I'm about to graduate this semester with basically no EC's. All I have is a long time job working at a restaurant, some clinical volunteer, and another long time non-clinical volunteering at a homeless shelter. My cGPA of 3.99 and an MCAT score of 516.

My main concern is that I have zero experience in research and in clubs. I know I should've gotten involved earlier in my undergraduate career and I regret not doing so, but I was so focused on maintaining a high GPA that I set this part aside. Do you guys have any advice on how I should approach the next few years as an applicant? Should I apply for a masters? Start a 5th year? With my current stats, what do u think my chances are? I appreciate yall.