attenuated and biased output from op-amp
It might be the probe attenuation.
Some probes have a switch on them that let you select an attenuation of 2x, 5x, 10x. Other probes are simply built to attenuate and don't have a select switch, but simply have a, say, 10x written on them.

To account for this, oscilloscopes have an option for each channel to specify what kind of probe is connected to it.
For example, if you're using a 10x probe you would select the 10x option on that channel, so that the oscilloscope can display the right signal. 

My guess is that you either are using a 10x probe without the proper option set on the oscilloscope, or vice versa you're using a regular probe with the 10x option activated on the oscilloscope.

If you multiply the output channel vertical scale by 10, you get 1V, and with that scale the output would be exactly twice the input (since the input vertical scale is 500mV).