Very informal, but "I owned that exam" to me would imply having done as well as possible.
Usage 3 in google's dictionary reference* states that the informal usage of "own" is: "utterly defeat or humiliate." Dictionary.reference.com** similarly defines it as: "to totally defeat, gain control over, or dominate in a competition: I totally owned the last two levels of the game." Both seem to agree with what I would judge intuitively, which is that you couldn't say you'd "owned" an exam unless you'd gotten full marks. The implication is "utter" or "total" defeat, thus perfect performance.
For formal usage, though, I would agree with those saying that "I got a perfect score" or "I got full marks" would be the most appropriate. "I nailed that exam" above is also a nice informal solution.
Interestingly, I think this discussion is showing a real difficulty in (at least American) English in distinguishing between perfection and merely doing very well. There's a lot of difference of opinion and usage around "Aced" for instance (for me growing up, it was always synonymous with "got an A") and I don't think anything has clearly emerged as completely unambiguous around a perfect score that isn't also awkward or not particularly idiomatic. Even my suggestion wouldn't be quite wrong in describing a 98% or 99%.