Given the question, there's two sections of Robert's rules that seem to apply:
From "Draw High" (section 12), #5:
Five cards constitute a playing
hand. Less than five cards for a player (other than the button) before
action has been taken is a misdeal. If action has been taken, a player
with fewer than five cards may draw the number of cards necessary to
complete a five-card hand. The button may receive the fifth card even
if action has taken place. More or fewer than five cards after the
draw constitutes a fouled hand.
From General Poker Rules (section 3), Dead Hands 1.d:
Your hand is declared dead if; the hand does not contain the proper number of cards for that particular game (except at stud a hand missing the final card may be ruled live, and at lowball and draw
high a hand with too few cards before the draw is live).
From that, I'd say your 4 card hand is dead.