Need advice- do I quit my job?

Hello! I currently work as a full time medical assistant and am planing on retaking the MCAT on may 14 to try and improve my score to apply this cycle. To study for the first MCAT, I worked full time and studied as much as I could for 6 months and only got a 503. I know I can do better as I wasn’t super productive during my last prep period and there are things I know I can improve on, one of which quitting my job to study. However, I’m feeling held back from quitting (probably because it’s a major change and, even though I’m perfectly fine with finances, am very worried about having no income for a few months). I’ll probably sub at a local high school once/week to have some form of income but am still very worried. Any advice would be greatly appreciated!