No. Sakura is not stronger than her master. Early on in the manga, it is noted by Kakashi that Sakura has quite a small reserve of chakra. The only reason she is able to mimic her master's strength is because of her excellent chakra control. However, we know Tsunade has an enormous amount of chakra, and even has some more stored up in her forehead. So no, Sakura is not stronger, or ever will be stronger, than Tsunade-sama.