I think "a key" makes it clear that there is one key, could be any of them, but you need to select one key. "Make any 3 key presses" would in my mind finally al

I think "a key" makes it clear that there is one key, could be any of them, but you need to select one key. "Make any 3 key presses" would in my mind finally allow QWE and QQQ.