LM2596 based buck design doesn't deliver power and heats up
The input and output capacitor need to be much higher.
Input = 680uF
Output = 220uF

At 3A you will certainly need a hearsink. This regulator burns a lot.

Replace 1n5824 with SK56. You can check the working design with LM2576 which is almost the same, except it works at 52KHz so it requires a bigger coil.