Suggest you add:
- series resistors in the data line going to the pixel rings.
- 100nF Decoupling on Vin and several on 5v
- decoupling at all power terminals.
- difficult to tell if the GND is going where it should.
- seems like the routing is weaving between the two layers more than needs to be.
- maybe diode in the Vin line for reverse protection.
- beef up the width on 5v traces.
- vias bigger.
- vias between GND plains.
- thermo vias under regulator.
- Nano pads could be bigger.
- how about some mounting holes?