Very worried...

Hello, I’m gonna be applying to McGill for the Fall of 2020 and I have a question about applying. I noticed that in the minimum grade requirements you need to have a B+ average for year 10, 11, and 12, B+ in each English, as well as a minimum of 28 ACT for the Arts. For year 11 I had a 3.55 gpa with a B+ in English and I’m certain I can do even better during year 12. However, due to personal difficulties and scheduling mess ups I finished year 10 with a 2.71 gpa and a B- in English. Would my poor grades in year 10 ruin my chances? Could an extenuating circumstances letter maybe help explain year 10 better?
Finally, when it says B+ average for Grades 10, 11, and 12, does it mean a B+ average for each individual year or for the 3 years combined?
If it helps I have a 31 ACT as well as a few 720+ sat subject tests.

Thanks for all the help!