Internship position got replaced

I got accepted at a company in 2 fulltime roles and 1 probationary role for a month to see if I'm fit for it. by the end of the probationary period I wanted to quit the probationary role and stick to the fulltime roles that I have signed a contract for, because I was being overworked af.

when the time came to talk to my boss, before I could even tell them, they said the teams of my fulltime roles are going to be dissolved and I will be taking on the probationary role fulltime (for the remaining 2 months).

I talked to my boss and they were giving me some copro talk when I voiced my complaints. They said I could take the role or I could quit, but they can't guarantee passing grade if I do quit (I had to take the internship as part of an industry training course at uni). I'm basically being threatened with grades and forced to do a role I wasn't supposed to do fulltime, and being removed from the role I did take fulltime. Is this legal?