I am recording through line in. I can hear both channels through headphones ( or speakers) so it is not my computer or connections. Balance is centered. The vu meter in PT only shows right track volume and that is all that is recorded. I chose audio stereo for the track I am recording on. This is PT2021 on windows 10 computer. This is a new problem as I have recorded this way before with no problem.

For many audio interfaces there is a right/left channel.
If you are only plugged into (only) the right channel this is expected behavior; you may hear it in both channels (due to panning in the audio interface settings) but the interface is still only sending the signal thru one channel to PT.

If this is the case I'd suggest setting the target track in PT to MONO, in which case PT will record two MONO tracks .. and then after recording, set the desired single MONO track to center panning.
And delete the other.

If PT only shows signal on the right side, then that is likely all it is receiving from the interface.
You may be hearing it in stereo during the monitoring due to the audio interface.

What Audio device are you using?