is there a chance that you finish med school and can't find a job?
Short answer: Yes
It depends on a lot of things though. After I graduate I have to match with a residency program. If I do match, then the specialty that I chose has to be fairly non-competitive for me to not find a job. However, I want to be a surgeon and I shouldn't have any problem finding a job. Especially with the ACA, there will be a lot more people seeking medical help so the AMA is actually predicting a shortage of doctors for a few years.
Edit: My national board score will also determine if I can get a job. If I fail the board one time it crosses out like 16 states I can practice in.