It is possible to crack JEE Main in 3 months with strategic planning and proper time management. Since you have less time, it will be better not to join coaching. Self-study will work better. Concentrate on Chemistry. It is the easiest and most scoring in JEE Main. Join a test series and give regular tests. Analyze the mocks given and work on the areas of your weakness. Solve previous year's questions and model question papers.
Obtaining more than 150 in JEE Main is not a difficult task. If you prepare with proper dedication and approach it won't be a problem.
Therefore, cracking JEE Main is not an impossible task in a 3 month preparation time. All you have to do is work harder than usual and avoid any kind of distractions like games, social media, etc. that consume too much time and energy.