Why is my amplification this little
The most likely culprits are R3 and R4, assuming C2 is 100 nF. You've missed the point that, although they produce an offset, they also interact with C2 to form a high-pass filter with a corner frequency of about 3 kHz. Generally, the amplitude of "real" sound drops off at higher frequencies. This is why, for figuring out gain, you need a sine wave generator rather than music. Try replacing R3 and R4 with 10k or 100k resistors, and/or replace C2 with a larger cap.