Fabio,
if you hook the top of the sail os it hangs lower, attach
the boom and the tack to the upper hole, and the
outhaul to the upper hole at the back of the sail. You
cannot roll the sail around the boom as you need to
attach the mainsheet. When the outhaul is tight, the sail
will be the right shape, but have a bag of loose sail next
to the boom on one side. Roll it up and secure with
shock-cord through the eyelets in the sail