I'd like to express the fact that there were no viable alternatives to a decision I took.
My decision to attend university X was stringent / without alternative / a no-brainer / objectively necessary because it was the only one offering the course in which I am interested.
I'm not sure whether stringent in this context is appropriate. The rest of the listed phrases in italics are passable for my taste but I'd like to use a single word to express the notion of having no real alternative.