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, etc.
Brain chatter happens to everyone, so do not get discouraged. Return your attention to your breath. No judging. Just come back to breathing and your breath. Every time you come back, you are exercising that brain/mind-muscle called awareness. It's like a bicep curl for your brain. This process is not something that can be rushed. Mindful meditation takes time.
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. Mindfulness doesn't mean we have no thoughts or create an emptiness. It means you connect in awareness, with the experience at hand, in a thoughtful manner with no judgment. Observe your presence and connect with the experience. Be an observer of what is happening to you, noticing your breathing, emotional state, and body sensations. Become more aware of yourself and how you are being affected. And remember, practice makes better!