I stayed late to get my work done.
Why did you have to stay late?
I don't think there is a justification, but I'm working on it anyway, and I'm not doing any harm to anyone.
It's good to work late when we can't finish our tasks on time. It's a very respectful thing to do.
I'm being too nice, is this normal?
It may be for you, don't beat yourself up over it! Kindness is a virtue and you are only doing your duty by making sure everything is on time. Your bosses and coworkers might commend and reward you for your dedication!