If you want to make it even harder, you could hide the grid until the user starts the quiz. You might need more time on the clock in that case, though, because one minute is not a lot of time. Fun quiz, though! Another quiz with pictures instead of text would be fun, too.
I figured out how to hide the grid! Putting this in your instructions box below the instructions will make it hide the grid. Just remove the spaces between style and the triangle brackets.
< style >
.pre-quiz .grid-container { display: none; }
< /style >