9v preamp for acoustic guitar

Hi kiwi, welcome to the forums
I don't see any connection to the middle pin of the JFET.
Also several connections that should be grounded aren't connected to the ground plane.
You also need to specify the part number of the JFET so we know its pinout.
Personally I would make the layout more compact. You can see that there's a resistor connected to each pin of the JFET; I would put them side by side, with the JFET at the end, and run three short straight tracks from the JFET to the resistors. Then add the other components.

 

Normally, wires have their own holes. And it's normal to put the holes for related wires in the same area, and connect them into the rest of the circuit using tracks. So, for example, the two wires that go to the pickup should connect to two pads that are next to each other.

That's the conventional way. You can solder wires to component terminals; this saves some space. But this makes it more likely that a wire will accidentally be soldered to the wrong point, and if the wire breaks off, it may be hard to see where it was connected. So it's best to have individual pads for the wires, and to put related wire connection points together.

In a commercial design, off-board connections would be made using plug/socket connectors.

Your new layout is better, but it still has errors. It looks like C3 is connected between the gate and drain of the JFET. R1, R3 and R4 aren't connected to the ground plane. Also, I think your resistor outlines are much wider than they need to be. Small resistors can be spaced at 0.1 inch pitch.

The MPF102 doesn't seem to be readily available. N-channel JFETs available from Digikey are J105, J106, J107, J111, J112, J113, PF5102. Mouser have 2N5485 and 2N5486.