To achieve your goal would require setting up Conditional Advanced Actions and custom User Variables. You need to use the On Focus Lost event of the Text Entry Boxes to trigger a conditional advanced action that will check whether or not the user has correctly entered text before allowing them to move on.
It may even be necessary to use multiple slides to gain even more control because then you also have the On Slide Enter event available for triggering more actions.
It's quite a complex thing to pull off, so you'd better be prepared to spend some time on getting it sorted out.
