The tetris piece stage has two parts. If you are in the first one (which is a mini tutorial that shows you the controls), you need to press Space while you are not moving to pass to the next part. So, before pressing Space, you need to press Down key so that the piece stays in place on the right side of the screen. If you are in the second part of the tetris stage (where you play Tetris as you know), the piece should stop when hitting the top-base wall (if it doesn't, it's a bug that I haven't experienced). Hope it helps you!
Thanks for the feedback, I really appreciate it!