Key practice
Send with a straight key and see what you actually sent. Your speed is not a setting — it is measured from your own fist, so a dah you held a little long is still a dah, and a dit you clipped is still a dit.
Hold the button, or hold the space bar. Stop for a moment and it reads back what you sent.
Nothing sent yet.
Why your speed is not a setting
A decoder that trusts a configured speed fails on exactly the input it exists to read: a person sending at “about twelve words a minute” is not sending at twelve words a minute. This one recovers the dit length from the signal itself, and uses the gaps inside a character — which no timing scheme ever stretches — as the ruler when the marks alone cannot settle it.