You scheduled the time; you found a quiet space; you closed your eyes; took a deep breath in through your nostrils and exhaled through your mouth - 3 times. You’re focused on your breathing. And then you start planning your dinner - the time you need to prepare, the ingredients, what you need to buy ...
Brain chatter happens to everyone so do not get discouraged. Simply return your attention to your breath. No judging. Just come back to your breathing. Every time you come back you are exercising that brain muscle - awareness. This process is not something that can be rushed. Mindful meditation takes time as this account will attest:
The student asks his teacher "How long will I have to meditate to attain serenity?" The teacher says, "30 years". The student says - "that is a long time; what if I work super hard, day and night, doing nothing but this?" The teacher replies, "Then it will take you 50 years."
So you see, meditation is easy but it's not. It's a special, personal practice that you master over time. Being mindful is another personal, special practice in which you take the time to be aware of your actions in that space and time. All of this work takes time and there is no rushing it - that is the part of the purpose!
Mindfulness doesn't mean we have no thoughts or create emptiness. It means you simply connect in awareness, with the experience at hand, in a thoughtful manner with no judgement. Observe your presence and connect with the experience and internally observance what is happening to you - your breathing, your emotional state, your body sensations. Become more aware of you and how you are being affected. And remember, practice makes better!