Will class 11 syllabus come in IIT-JEE as my concepts are weak??

yea it will surely be asked.. both class 11 and 12 are mandatory for iit-jee exam. you can find detailed syllabus over here  : http://www.askiitians.com/iit-jee-syllabus/pattern-iit-jee.aspx

It is really important.Without 11th syllabus you cant even think of IIT.If you are not getting class 11th concepts right,use D.C.Pandey physics,O.P.Tandon chemistry and arihant series maths.They will do your work