Common-practice voice-leading conventions are rules of preference—each one a reflection of contemporaneous musical practice (i.e. “style”). Music theory is not designed to prescribe them; it can only describe them.
If your harmony teacher were to say that something about your part-writing assignment is “wrong”, it would suggest that your solution is inconsistent with common-practice conventions, not that there is such a thing as “right” or “wrong” music—a stubborn misconception about the nature of music theory.
Put another way: a 7-line haiku hasn’t necessarily stopped being a poem, it has only stopped being a haiku.