You have more to gain by making it Open Source. Respect in the community, reputation and the contacts you will make are worth more than the few $ you might (read "might") make. If you did this work at a public university then likely the public owns the software and you can't legally sell it anyway.
If you do sell it outright, a smart buyer will know only to pay you the profet he expects to make (that's after his expenses to market and support the program) but he will add a BIG multiplier for "risk" and then reduce the offer to include profit for himself. Do the math and you don't get much. that "risk" factor is huge and squashes the value of your work. Do something to reduce that and you gain a lot.
Also remeber any sucessfull bussines will require some investment. You will need to pay for marketing. You will also need to file taxes get a bussnes licesnse and so on. Maybe hire an accountant to consult with.
Think about insurance, payrol taxes and so on too. If you are so small you can just ignore all this then you are working for less than minimum wage and would be bettr off with Open sourse. Don't bother selling software unless you can make $50/hour because.
Yes I have had software I've written paid for. But through my employer. How else to support wife, two kids, house, cars, sailboat, travel hobbies pay for kids education,..and so on. But doing it myself as "shareware". I'd literally make more money at Mcdonalds selling burgers. Literally. How many hours have you invested so far? Double that to get it to market and figure how much per hour you worked for. It is minimum wage? If not the fast food industry pays better. On the other hand you have a lot to gain by being the leader of a successful and popular Open Source project. Networking with many peers will pay off big later. At your age think more about investing in future payoff then making a couple $ today -- that's what school is all about.