As someone who's grown up in a Muslim household myself, I understand your situation. However, before I dive any deeper, I first want you to understand that you did NOT fuck up by owning up to it and telling her the cold hard truth. It's probably the best thing you could've done in your situation, and I respect you for doing that.

One of the problems with most parents, particularly the conservative type (I actually don't know how conservative your parents are mind you), is that they tend to hyperbolize their children's shortcomings. Whenever a child fucks up, instead of sitting down and having "the talk", the parents will give off the vibe that you're committed the most horrible of atrocities imaginable. You mentioned that you had a verbal exchange with your mother ending with the "work hard and focus on your studies" bit. I'm not sure how well she communicated the situation, or whether she addressed the elephant in the room in the first place regarding the alcohol, but I guess you could count that as the talk. The way she's acting afterwards however, is not healthy for the child. I'll get to that in a bit.

Her reaction is quite natural. She's understandably upset that her child has deviated from the path she set out for them. Anyone would be in her place; I don't blame her for that. But at the end of the day, you as a parent should understand that children will fuck up. It's not a matter of if, but when. You gotta build that mindset when raising one, something that parents in this side of the town unfortunately fail to grasp. Your job as a parent in this situation is to guide them in the right direction. Whether they take that guidance afterwards is on them, and they'll have to live with the respective consequences (this is also something they have the responsibility of making abundantly clear to said child).

The tactic your mother's employing however, partly borne from her own emotions, is to build up a mountain of guilt in a passive-aggressive manner that devastates you. It associates this extremely negative (often traumatic) patch of memory to an indulgence they do not endorse (in this case alcohol) to ensure you recall said moments when committing to said indulgence again in the hope that triggering said memory will discourage them from doing so. From experience I can tell you that only works 40% of the time. Regardless, what I want you to take away from this is: don't think too hard into it. It's just the way some parents handle the situation, and your mom happens to fall into this specific category. Some parents would approach this better, others exponentially worse. Deal with this in a mature way, but don't let it get to you.

Let's put your family and friends to the side for a second and focus on you. Look, you're 18. This is THE prime time for you to experience everything this shithole has to offer and grow yourself as a person off of that. This is the part of your life where you'll be making the shittiest of life choices and learning from them. Just don't go in too deep. Be mindful of which path you're treading, and make sure you're in a spot where you can pull yourself out of the situation if it spirals out of control. The way you do that is by striving a middle ground between your vices and the values you were taught by your parents and the religion that you reluctantly committed to all these years. Whether you choose to be a man of faith or not down the line, always learn to respect these teachings in the brief time you were remotely attached to the religion; the reason being that the ideal lifestyle any religious practice strives is that of stability, and therefore offers a reference point that you can always come back to when charting a course. Maintaining this stance helps you grow to be a wiser person without drifting off the deep end.

You've got your whole fucking life ahead of you fam. Treat this as a learning experience, but don't let it weigh down on you too much. Keep doing what you're doing at university and work. Show your mama that you're growing up to a responsible adult and that you got your shit together despite the vortex of all the unhinged shit young-adult life has to throw at you. Regardless of what happens, I hope your relationship with your family only gets stronger after this farther down the line. It might not feel like that right now, but give it a few years, and both you and your mom will be laughing your ass off about it.