a fellow ib student!
i too am going through this struggle. i was bounced around the various mcmaster departments for the better part of an hour before i got someone who was even remotely interested in helping me.
i managed to do fairly decent and get the required 33 (a shock to me) for them to look at me for engineering courses... but all i want to do is take off those complimentary study electives... i still want to take chem because i dont think we covered all of it that the 1a03 course goes through... though we did a fair bit.
so i called them. registrar->engineering faculty->registrar->high school liason office->faculty of engineering.. a couple more bounces and then back to the faculty of engineering finally.
so the lady i finally talked to said that she would send me an email when she found out what to do (i dont think they get very many ib students). so in her email she said that i needed to setup an email with a lady named sally williams at the beginning of september. they dont have the ability to do anything before then. perhaps if you called the university and asked for her specifcally she would be able to help you.
in your specific case.. im not sure exactly what to do because you need to have it taken care of. i would call the university on the off chance you get someone who knows that theyre doing with regards to ib.
and higher than six in hl chem... my hat is off to you sir.