is jee mains maths tough or physics if I have to study among these only one which one should I choose and will be goid scoring in just 45 days

Hello,
To prepare for JEE mains and score good, you need to do justice to all the topics of the syllabus for JEE mains. But as you have less time now, and to atleast clear the cutoffs for jee mains, you can clear the topics which have the more expected weightage. Please note that, JEE mains chapter weightage is not always accurate as the authorities of JEE mains might change the pattern every year. But you can be in the safe side if you atleast get an idea from it.
Here's the link for JEE mains syllabus with weightage. https://www.google.com/amp/s/engineering.careers360.com/articles/jee-main-syllabus-weightage
Hope it helps