Turning down a salaried position in retail to continue education?

I (F20) have been working full-time at the same big box retail store for 3 years and was recently offered to become a store manager for a new store opening near me, starting salary $80k (USD) with potential bonus of up to 20%. Currently I make about $50k a year as an hourly full-time associate. I have made good connections while working here and two corporate managers have put my name forward not knowing that I plan on leaving the company soon. The past month, one of the managers has really been trying to sell me on the position and it's starting to convince me. I have been working full-time and taking a full course load the past three years, but it wouldn't be manageable with the promotion solely because of the time I would have to spend at the store. Aside from that, the job is easy for me but mentally draining.

No one knows that I am stepping down from my position in April to finish my degree in urban planning and fully dedicate my time to pursuing internships and networking. I have kept it quiet to keep my options open (which seems to have worked a little too well.) I'm set to graduate next year and I know that urban planning is what I want to pursue, but even a gap year or two to take the position and make that amount of money would probably change my life. It would also be a secure job, and the job market for planning, especially in my city, is highly competitive with very few positions. I have decent savings and plan on staying part-time at my current store so I am not in desperate need of money, but $80k a year could help me buy a house for my parents and be even more financially secure.

One of my professors in the past talked me out of taking a gap year when I first started working full-time because retail is always "desperate for people" - ultimately I think I am worth more and I can't work for this company much longer, but am I making a mistake turning this position down in this abysmal job market?