Help please

Please whoever is reading this I am in need of great help.
My family applied for Canadian immigration and our Canadian visas have arrived.
The biggest problem i am facing is regarding my education.
I am from Pakistan and am doing first year of A-levels.
But due to the immigration my family has to move to canada by 9th January.
Will I have to attend highschool in Canada? And will I be able to join it in January or August?
Also is it possible that I don't immigrate to Canada and complete my A-levels?? Will this action ban me from Canada?

Please reply, if you have been in a similar situation please do reply, I beg of you. I really need help