May I make a few suggestions to make things nicer and cleaner?
Simple basic rule when routing PCBs: keep traces as straight and as short as possible and use as few vias as possible.
You have some unnecessary bends in traces that could just go straight, making them longer than they need to be.
Also try to pay attention to giving things a bit of space instead of having traces wrap around the keepout area around pins and solder pads - use the raster instead to cleanly route them through in between two pads keeping as much distance to the pads itself as possible.
Also for each signal layer decide for a general direction the traces should go... For example stick to mostly horizontal traces on the red layer and vertical on the green one - or vice versa.
If you're not doing that you end up with way more spaghetti than necessary and you'll have a lot of traces just passing short distances over/under each other which means you'll need more vias.
Those are some good and simple practices to get used to right from the beginning. It might not matter much on low speed and simple boards like this one, but as soon as space gets tight and you're doing more than 4 layers vias are going to take up valuable space that you'd need for traces.
Also from looking at the ratsnest it might make sense to turn the CPU by 90° counter clockwise or the FPU by 90° clockwise to make things easier.