Why in 22Na spectrum is only one backscatter peak evident when we have two of different energy (511 keV and 1275 keV) gamma rays in the spectrum?
However, your crystal can be quite bad and you see like one large bump. I remember old crystals having 700 keV resolution. Nothing to do.
the tension is too low
the MCA is not properly set and maximum of the signal is not recorded (gate)
if you have a digital acquisition, you may need lot of work and understanding to tune correctly
Edit: 1. the picture is an illustrative one taken from i.stack.imgur.com/n0BzJ.jpg. Purpose is to give a hint how such a spectrum can look. The author of the question did not see anything reasonable up to now, nor he posted a picture.
The labeling is not mine, Compton edge label should be also at 1000 keV near the photopeak.
I modified labeling a picture a little bit.