You know you want to own your own company, but it sounds like you don't know what type of business you want to go into.
So, I say, take the position, research Economics and Finances on your own valuable time with the goal of learning about personal and business financial management (on a global and local scale), research entrepreneurship resources, etc., and find out where you would like to go.
Meantime, use the 9-5 job to A) pay off your debts
B) SAVE SAVE SAVE SAVE AND BE FISCALLY CONSERVATIVE (yea, you may be able to afford a new car now, but in todays market, it's best to invest in a reliable cheaper vehicle and/or public transit)
C) Search and think of business ideas (Brainstorm, Brainstorm, Brainstorm!), and write-up rough drafts or even final drafts of different business plans (or business plan proposals, simply a catalog of business ideas u have)
D) And NETWORK NETWORK NETWORK: Businesses arise from either 1) Inventive new product service development (think iPhones for example), and 2) Needs/Solutions Supply (computer technician, auto repair, financial consultation, for example). Now, as much as #1 is more your own personal project, the answer to #2 could come from peers who you talk to about problems, colleagues, or event customers who vent about something they hate or would like. These are where you can find business ideas.
And also, above all us, go what I call, "Live by your Goals" and give yourself deadlines to when you want to be ready to leave your 9-5 and start your business full-time.
9-5 aren't bad, just not the retirement plan for most of us of our generation. But, it is a need for us temporarily, unless we're lucky and created a hot idea like Mark Zuckerberg, founder of Facebook.com, or we come from the sperm of Donald Trump and friends. So, get that job and let that be your cushion for a while
"To walk in the shoes of a successful fellow, you must first walk in your socks to his shoe store.