> but there are days in which I feel like I really can't do anything and basically idle until it's time to go home, and this last part is really killing me with guilt.

This is internalized capitalist serfdom right there. You are in a business contract. If it’s not your fault you can’t do anything useful, why the F feel guilty? Best thing you can do - if I may suggest - is to use that time to find a better job. Sometimes a job doesn’t work out, don’t beat yourself up over it and learn the signs.