Don't sweat it. I did an amplifier calibration and was sure I had an awful amp. Until I realized the scale was only 4 db. When you zoom out to a 40dB scale, the amp looked perfectly fine
Also, the new version of REW can use a loopback from the unused channel in your soundcard to auto-calibrate. No cal file needed. I think it's a great feature and can even out any non-linear problems with a soundcard (like maybe the calibration changing with input levels or something similar).