Never ever set an aim. You never know if the paper is tough or easy. It just adds on extra pressure. And I know you kept your expectations in check while aiming for those particular marks in each subject. But I think everyone should be optimistic and hope for the best. 150 marks? You can cross 200 if you utilise these 6 months judiciously.
Coaching helps to give you the competitiveness and atmosphere. Not much more unless your teachers are great which in my case weren't. You can get that by practicing online mock tests. Buy resonance or allen online test series(it really helps) and nowadays they conduct computer based exam mocks at centers in live environment as well. Just enroll in that. Its not that expensive either.
Some tips for mains:
Physics: For chapters in which you think you are good at, just solve problems. Solve DC Pandey or HC Verma or any material.
For chapters in which you are not confident in, just give yourself the pleasure of reading HC Verma Theory (that book is famous for a reason, explanations are simple and from the basics and not too long as well!). Once you get a grip of theory, then solve questions. Dont solve higher problems like level 5 or fiitjee aits from such chapters, just make sure you are able to do most of the previous year questions. If you do as I say, you will cross 70 easily.
Chemistry: NCERT is sufficient to score 80 marks and as a guy who was also a dropper once, thats not a hype and its true. Just stick with NCERT and previous year questions.
Maths: Only one thing, practice. There are no shortcuts in Maths in terms of practice. Once you get the formula and the concept right, start doing level 1(easy) problems to comparatively higher level(but not too high!). You must climb that ladder especially if you are weak in a particular chapter. For some guys maths is natural, while for others it might be tiresome, but you must be ready to put the extra effort, it will bring you success like you had never seen before.
Whats common in all three?
Must complete previous year questions. You could do like practice all the previous year offline papers from a book like Arihant 40 years and then do previous year online papers as mocks. But you must practice them. You are bound to get similar questions.
As a college student, I would say put all the effort you have in these 6 months, after these 6 months, you will feel proud and relaxed and bindaas because for me personally, though college has different challenges, it is nothing compared to JEE.