Give up Supervisor Position for a BA Business Studies and Marketing?

Hi everybody.. Here is my predicament..
I am a 20 year old Supervisor for a well know watch brand in bluewater. Ive been told that i have a "very bright future" in retail and management and been put on a fast track management programme but i want to go to business and marketing. Cut a long story short, i applied for a marketing assistant position internally and i didn't get an interview although i've been there for 2 years because of my lack of experience. I don't feel i can get into a field of my choice without a degree to stand me out of the rest of the applications.
I came to Christ Church yesterday and it seems good, nice and friendly place to study. I just keep getting doubts whether it is the right decision to leave what i've accomplished in 2 years to study for 3/4 years and have a better chance of getting the job i want.

Any thoughts welcome! Thank you.