How much trouble do you think I'm in with my mom?

So it's 3am, I overslept from my nap and I have a 3 week essay overdue by 3 weeks that HAS to be done by tomorrow. I smoked a spliff out my window for motivation, come back in and get started. 5 mins later my mom comes out of her room an says 'nade, I don't know what you're doing in there but it stinks and it's woken me up. It smells like drugs and I don't want you doing it in my house.' she said it in a really stern voice.. Thats when I realised my room is completely filled with smoke an it smells sooo strong! Thing is my mom has a reallyyyyyy short temper and it doesn't take much for her to go off the handle, surely the lecture she gave me is just a prelude to the real punishment? How should I handle this? Shall I explain that I like doing it like both my brothers drink, but I don't, I smoke pot? Or should I apologize and vow never to do it again even though I probably will?