It's not a problem - that's literally the practice. You focus on something like your breath, and every time you catch yourself getting lost in thought, you just gently go back to the breath.
The overwhelming majority of people couldn't stop their thoughts for even 10 seconds if their life depended on it. And they don't have to. Just notice the thoughts and start again.
You can even meditate on the thought itself - it doesn't have to be the breath.