It's hard AF but they accept people every year. Your competition is the rest of the enlisted Marine Corps that has a degree. They take around 15 a year. For 2018, there were 183,501 Marines, roughly 77% of which are enlisted. About 2% of the enlisted force has a bachelor's degree or above. So that's about 2,826 potential applicants for 15 slots.
How do you figure you stack up against those other applicants? Beyond having the degree, what's your GPA? What's your leadership background? Leadership experience is HUGE to Marine Corps officer selection. How are your fitness scores? How are your performance reports, etc.? Your whole person is considered in the process, so consider how you stack up against the rest of the USMC enlisted force as a person. Are you a leader other Marines want to follow? That's really the question that concerns the selection board. Your package is proving to them that you're that Marine.