If you are applying on the basis of a 2nd bachelor/alternate degree:
You have to complete your primary bachelor degree. That means, you went to graduation and you received your diploma. I think you're all set on that.
Now for your 2nd bachelor/alternate degree, you must have 45 consecutive credits or more before Nov. 1st of the year you are applying and you must have completed your diploma ( finish all your classes) before July 31st of the year you will be starting medical school and you must confer your degree before you start medical school (receive your diploma before the first day of class at medical school). That means that, regardless of the 30 credits you did in program X, they will not be considered by med admissions unless you complete program X. Therefore, you will need to graduate from program Y, and only this degree will be considered as your second degree.
Alternatively, you can finish program X if your cGPA is good. It will be quicker than starting a new program and having 30credits that do not help you get admitted.
The main point is : you're eligible for McGill Med, you got to confer(graduate from) program Y to get a 2nd degree and you must respect the deadlines. https://www.mcgill.ca/medadmissions/applying/requirements/requirements-edu/degree-requirements