yeah.. if you have an arduino with the capability, using the keyboard class like this is a very bad idea... As the doc (which you probably did not read) states
A word of caution on using the Mouse and Keyboard libraries: if the Mouse or Keyboard library is constantly running, it will be difficult to program your board. Functions such as Mouse.move() and Keyboard.print() will move your cursor or send keystrokes to a connected computer and should only be called when you are ready to handle them. It is recommended to use a control system to turn this functionality on, like a physical switch or only responding to specific input you can control.
When using the Mouse or Keyboard library, it may be best to test your output first using Serial.print(). This way, you can be sure you know what values are being reported. Refer to the Mouse and Keyboard examples for some ways to handle this.
you might get lucky holding the reset button down and letting it go just when you see the message uploading code in the IDE (upload the blink program - not yours again of course !)