First thing is that Not all those who qualify JEE Advance are extraordinary in Physics and Mathematics, They are Just able to solve Physics and Mathematics Problems of JEE Advance level, which they could due to practice they do, therefore if You think You are Good at Mathematics and Physics then Yes You can qualify JEE Mains as well as Advanced , Just practice some Previous Years question and check whether You can solve them or Not If You cannot then you need to practice more.