A large number of kids join law firms from college since they think getting a job in one evidences that they made good use of their time in college. Once they join a law firm, many realise that this isn't what they want from their life and they quit, and that's fine. If you think the trade-off is not worth it, then leave - and, ideally, leave early. Try your hand at something else when you're still young and don't have any significant financial obligations and generally fewer responsibilities.

I don't want to increase the pressure you must already be under; but the threshold at which a person is warned that they may be fired is really high. This isn't the IT industry where lay-offs are common - traditionally, law firms have never done large scale lay-offs in India (or, for that matter, globally). So long as you put in the hours and show earnestness, I have seen absolute bumbling idiots hack it out in good law firms and climb the ladder, albeit, at a slower pace.

So, I would take this warning seriously and buck-up if I were you. The "management" will not listen to a fourth month A0. Speak with your senior or the partner and ask them how you can improve your work product and your attitude, if that's what they think is wrong, and then make a concerted effort to improve and ask for regular feedback. Separately, also speak with someone from your college in the firm who you know personally and see what you can do to improve. If you aren't willing to give it your 100% then you should really consider leave a law firm and doing something else, unfortunately, this line of work requires a strong work ethic and longer hours for the first few years. Things do relax a little bit after 4/5 years of work ex.