It sounds, then, like you would apply for the MARCH I. MARCH II's are for people that already have a professional degree (here in the states, that professional degree is called a Bachelor of Architecture, or BARCH, and takes five years to complete). Because you are in the fourth and final year of an undergraduate Architecture education, you might be eligible for Advanced Placement, which varies in some of the programs (it might chop off a semester or two, depending on your degree and the program you attend). So basically, it looks like this:

1. People that have undergraduate degrees in completely unrelated fields (like, say, philosophy, biology or business) = M.ARCH I, and without possibility of advanced placement.

2. People that have four-year undergraduate degrees in Architecture (such as Bachelor of Science of Architecture, or Bachelor of Arts of Architecture), but it is not considered a "professional degree" = M.ARCH I with possibility to achieve advanced standing.

3. People that have a five year Bachelor of Architecture degree (a "professional" degree) = M.ARCH II.

I'm sure that there are other people on this forum that were in your same boat when applying, and might be able to weigh in with additional comments. Regardless, good luck!

Of course, too, I'd recommend contacting the schools to which you're applying.