New Quarter panel buckling at body line

I am welding in my new quarter panel and it's buckling at the middle body line (the line below the gas cap) to the left of the wheel house on the driver side if there is any pressure in the area. I have to pop it back in place or it will stay pushed in. These are the cheaper quarters made of thin metal. Can I weld in a support bracket in the back as long as it doesn't interfere with the operation of the quarter window? Would hate to have to cut the whole thing off and have to get the amd ones.