to make wavy hair straight, you will have to blow dry it.
get a straightening balm...and run it through your hair from roots to ends. Get a round brush and blow dry it section by section. Its a pain in the ass, but with your hair it shouldn't take too long. My hair takes 1.5 hrs to blow out!!!
tip... get a good balm, go to a beauty supply store or salon...good ones I can think of off hand...aveda hang straight...phytodefrisant...grahan webb's stick straight....etcetc