What really helped me improve my typing speed is not focusing on the content of the quote. No matter what you do, do not think about what you are writing, it will distract you. It's happening right now isn't it? you are messing up aren't you? Well try not to let it happen again and you should be fine.

My tip to improve your typing speed is to concentrate on accuracy over speed. There is a time between when you have learned to touch type but are not yet that fast when you plateau for a while. Usually the solution to this is to focus on accuracy over speed, many people push to be faster instead sacrificing accuracy that inevitably leads to a brick wall in terms of progress.