Magic cannot change your species,
can't make you grow taller,
can't make you loose weight,
can't change your eye color,
can't change your age,
can't change your skin color,
or anything else of the sort.
(Taken from Amichai's profile)
...Gender is included in that.
You could ask one of the teenage experts on here who are vampires, mermaids, control the elements to the point it rains when they cry or burst schools into flames when they are angry, or who have became a master in their path by teaching themselves in a few short weeks, they will tell you they can do it or give you a spell to do it, then claim you've done it wrong when it doesn't work out.
I don't know your reasons for wanting to grow that extra 3", but take it from me that if anyone has a problem with your height then tell them to take a running jump because they aren't worth a second look, I think petite woman are far more attractive and they get a lot more attention.
I doubt very much there's any spells that can acheive that, I'm a small person myself but im quite happy with my height I dont want to be taller plus the fact I can buy shoes out of the kids deparment so get them much cheaper lol!
But as for the height problem the best thing you can probably do is look into what clothes suit your body and make it longer and wear high heels(if your comfortable wearing them) and check up on which vitamins are good for growth ect, but with being 21 you've probably reached the tallest you're going to get now.