Unfortunately I am not very good at guessing where I made the mistake. The only think I can do is replay the lesson over and over again. I'm now on my 5th replay of one lesson Arrrgh!
An average will be close to 50 to 70 exercises for one lesson.
You obviously passed the time that you did Morse code right out of the womb, by saying dahdah dahdahdah dahdah to your mom.
Furthermore: What is the sense of using a keyboard to type the code, in general you don't have a keyboard available when you hear accidentally Morse code. (birds, doors, car-horns, a field day, visiting another ham)
So copy by a pencil during learning all characters and after that period in your head. Only one out of ten exercises typing over from your paper in the keyboard in order to get a score will suffice. It is written here often in the past. But right, it is easier to ask.
Suppose somebody is talking to you and you have first to print it out or write it out in order to understand it, you should have a hard life, shouldn't you?