In my country there are professional courses which give a qualification level of 4 and last for 3 years. It's part of the course to do an internship in the second and third year in which you can choose where to go or let the school choose for you.
In my case I took a programming course and as for the internship I let the school choose because I didn't know where to go. I ended up in the company with more ties with my school because I was the best at programming in my class as well as on school itself in both years.
In the first year of internship there were 10 more interns. In the middle of it they gave me and two of the other interns a task to develop a WebApp for them and so we started. The thing is one of them only knew basic Java while the other knew nothing at all, so I ended up doing it alone while the one that knew Java was trying to make an Android version. We never finished the project till the end of the first internship which was 2 months.
At the end of the first internship the boss called me to talk. The conversation went like: "You make projects for us while you are in school, we pay you for that". I gladly accepted cause it looked like a good opportunity.
Now almost at the end of the summer break we spoke again and they wanted me to do the Web App for free as it was an internship project so I thought that I'd only going to work in that when I'm there in the internship.
Fast forward to today, where I'm in the internship again, this time alone, and I'm rebuilding this big Web Application from scratch (because there was a lot of unnecessary stuff in the old one and I wanted to rebuilt it properly). All of this is being done for free and this application might give them some good money, so I can't stop feeling like I'm being used and that they might take this project for free and don't give me any more projects at all afterwards.
This begs my question: is this something usual where they're using the Web Applications as a test to see if I'm any valuable? How should I proceed? I thought that maybe as a safeguard if they do screw me over I take the project down and re-sell it, if so should I do it?
Sorry if the english is bad and if it's way to confusing to read, or if I made this question in the wrong place, please do tell me if I did.