Guitar signal with opamp boost
Guitar pickups have a high output impedance. The should be connected to a load with a high input impedance - typically 100 kΩ to 1 MΩ. Your pre-amplifier has a 1 kΩ input impedance so there is a large voltage drop across the internal coil impedance.

Try increasing R1 and R2 by a factor of 100 and see what happens. Let us know.