I'm experimenting with 4 layer boards to teach myself how to do it. I'm using a board that was previously a 2 layer board for this. I set up the layers as [21*2*15*16):15] and made layer 2 the VCC layer and layer 15 the GND layer then routed the board. The DRC check gave me a lot of layer setup errors, but I don't know what those errors are. I've attached a screenshot of one of them. I'm open to any tips.
I've no plans to send this board to a board house. I just wanted to see how small I could make this PCB.