When my fingers hurt after too much time on the keyboard, I take a short break and fix my posture before starting again. I wouldn't stay on for too long, and my advice is to be less tense and welcome mistakes at first.

When my fingers hurt after too much time on the keyboard, I wouldn't stop until I knew I was nearing the end or that I kept messing up!

My tip to improve your typing speed is to take your time with the typing at first, don't focus too much on your speed, but on your accuracy. Improve that first, then you'll be comfortable with keys.