I am trying to wire three way switches with multiple light between them. I have 12/2 from the panel to the first switch then 12/3 through all the lights.

At the last light I switched the common and neutral to supply power to the end switch.

From the first switch I can control all lights (5 of them). From the end switch I can only control the last light on the circuit.

What did I do wrong?

The 3 wire should run between the two 3 way switches, then a 2 wire can go from ither of the switches to each of the lights.

What you did wrong was mistakenly run the 3 wire to each light. 3 way switches need two wires alone that must connect between the two switches , called travellers. A 3 wire between each light only leaves one wire left over, and each light needs two, a switched hot and a neutral.

I have attached a picture of a 3 way-4way setup, Just imagine the 4 way is not in the picture.

Hope this helps.