I completely see what you mean - the current rules aren't entirely explicit.
I would suggest this rewording:
Your heroes prepare for the next challenge.
If you have fewer than 3 cards in hand, draw cards until you have 3 again.
I don't want to explicitly rule that there is a maximum hand size - there's potential for future cards that let you draw more, in which case Take Stock just specifies that you wouldn't draw more if you already had 3 or more in hand.
Does that make sense?