I'm eligible to graduate in Spring 2015 but have deferred my convocation until Fall 2015. I still want it to be that I've graduated in the Spring because grad school needs my bachelor's degree to be accepted. Does anyone know how to fill out the GIC if you are graduating but going to the convocation in the fall?

You can't defer graduations anyway, only attendance to the ceremony. See here: http://registrar.mcmaster.ca /grad/defer/