For real though, focussing something like that is not easy. Unless you're measuring your angles really carefully you're probably not going to create a death ray.

There have been some attempts (including a couple by Mythbusters) to replicate the legendary heat ray of Archimedes, but it looks somewhat implausible with the tech of the time.

https://en.wikipedia.org/wiki/Archimedes%27_heat_ray

However Richard Hammond did have an toy experiment at Keck with a mirror with a diameter of about a metre and did have some success: https://www.youtube.com/watch?v=ix_tsqKzkrQ&t=3384