Can anyone help me out??

Last year I add an cr/ncr to my eco100, the reason is that I totally can't follow the professor up in every lecture even I can't drop the course since it's corequisite with rsm100. I am not rotman student but I just took rsm100 without any reason(I don't even know why I took this course) Then the question is, if I change my decision now to want to enrol in economics subject post, can I do eco100 again next year? Is economics at uoft is limited enrolment, I mean if that you are not guaranteed to be enrolled if you only meet the minimum marks? Really need some advice!! THX