How to do my thick wavy hair?

okay i have extremely thick hair and im 11 i want to make my hair lie flat and have it not be such a poof i seriously hate when it goes poof nad i have little hairs in the front of hy head so when i put hy HAIR up it stands up really badly nad i put gel hairspray moose but nothing will work and to un poof my hair i use the frizz taming serum but nothing work im thinking of getting my hair thinned next time i go to get my HAIR cut please when i do my hair it doesnt even look like i try do brush it my hair cant be tamed