Many people have a mistaken idea that becoming blank is the goal of meditation.
Finally, and perhaps most importantly, remember that mindfulness meditation is about practicing being mindful of whatever happens. It is NOT about getting ourselves to stop thinking. Repeat: it is not about getting ourselves to stop thinking. It is easy to fall into believing that that is the goal. Many people have a mistaken idea that becoming blank is the goal of meditation. Perhaps it is in some approaches, but it's not in mindfulness meditation. So once again: if you find you are thinking (and you will), include it in what you notice. Don't try to get rid of your thoughts. It won't work and it's the opposite of the spirit of the practice. We are trying to be with ourselves as we already are, not trying to change ourselves into some preconceived notion of how we ought to be instead.