Hey,
It is not necessary to attend some sort of coaching in order to clear any exam and JEE Mains is one such example.

If you are good with your NCERT's and have your basics cleared about each subject then JEE Mains would be a cakewalk for you. 

The only thing that you can add to your preparation now is that you can go for some online test series and keep practicing as much as you can. Don't worry if you fail to attempt good on few days as it happens and you should take it as a learning rather than a failure because the only thing that will count will be your performance on the D day.

All the best :)