Hey there! You don't need to hold the keys needed to create the pattern — you can press the buttons one by one. The thing is that you have create the pattern in more or less half a second, depending on the buttons pressed, as seen through the horizontal bar below the control grid (small 2x2 boxes). It supposed to mimic the mechanic of touchscreen swiping, the horizontal bar going empty symbolizes that you are done creating the pattern.
I hope this clears up any confusing parts and I encourage you to give it another try. Thanks for checking!