Does eye strain from watching tv in the dark worsen astigmatism?

No. Astigmatism is an intrinsic property of the lens and cornea. Watching tv in the dark is no worse than taking a walk outside. You may have some glare but this should have no effect on astigmatism.
No. Astigmatism is a result of the shape of the cornea. While eye strain can be uncomfortable, it does not cause permanent changes in the corneal shape and therefore does not change the astigmatism.