I would tend to agree with pzabbythesecond. If McGill is the only school you are planning on applying to then my personal suggestion would be to proceed with great caution regarding the LSAT at this point if you are looking for the most attractive way to present your application. I'm not sure how your GPA converts into a 4.0 scale, but a 3.79 is very impressive on face value and it sounds like you have some great additional extracurriculars to bolster your application as well.
From my personal knowledge anything below a 160 (maybe a 157) would not been seen as positive towards your application. Keep in mind that McGill does not require the LSAT and does not discriminate against applicants for not writing it. However, if you do choose to write it, regardless of your score, there is no turning back, you will always have to disclose it to admissions.
Another thing to consider is that if you do not write the LSAT McGill may take it as a sign that you are very serious about McGill in particular as you could not apply to any other common law schools without it, so that could potentially work in your favour as well.
I don't want to discourage you from the path that you are taking for yourself, I just hope I could provide some insight that I have acquired as a successful applicant and current McGill Law student.
My advice at this point would be to convert your CGPA into the 4 point scale McGill uses and see how you sit on it. If it ends up being significantly lower, then maybe it is time to put the petal to the metal on studying for the LSAT to see if you can bump up your score, but otherwise, I would channel your energy into preparing a stellar application without the LSAT.