For clearing the JEE mains exam without coaching the first think you have to do is start preparing the previous year question papers for the JEE Mains
Second thing is that you should have a tight grip on the concepts in the NCERT and you should solve all the questions of the exercises and the miscellaneous exercises of NCERT of the P,C,M thoroughly
If you are following from some guides like Pradeep or or any other guide then go to their competitive section and do the daily practice from it and yes do not forgot to follow the HC Verma for the Physics it would surely help you.
It doesn't matter whether you are from jac board or cbse board..the thing that matters is how well you can study.Yes you can clear jee mains without coaching but it will require a lot of effort and dedication. You have to first clear your basic concepts from ncert books.And after that you can refer to op tondon for chemistry,hc verma for physics and arihant or rd sharma book for mathematics.After that you have to solve previous years questions for practice and to enhance your skills.Don't it can be done in 3 months.
Be motivated.Take guidance from your teachers and seniors.
All the best:)