Target creature gets +3/+3 until end of turn. It gets an additional +2/+2 until end of turn for each card named Growth Cycle in your graveyard.
Because Growth Cycle is still on the stack as you perform its instructions, it isn’t in your graveyard and won’t add to the bonus the creature gets.
The size of the bonus is determined as Growth Cycle begins to resolve; it won’t change later in the turn if the number of Growth Cycles in your graveyard changes.