No. Mystic is what shamans become. Once you chose druid at lvl 10 you were locked in to being either a fury or a warden.
Follow through with Fury! You're close - check it out. Furies are fine healers. Shamans do not heal better. They can slow mobs and make them do less damange, but Furies can buff the party's agi and stuff - and cause mob hits to do less damage. The priests are all very well balanced - so well balanced that there is almost no difference between them. Furies become lions, Wardens become wolves, Mystics become bears - Defilers become evil spirits... that's about the only real differences. Well, there are others, but overall they all pretty much balance out. If yer all the way to lvl 19, go for it! What's a few more lvls, anyway? Play up to lvl 24 or so, and if u really can't manage it, reroll a toon then.
But again, furies heal fine. Just remember to buff yer group and debuff the targets, unless that draws too much agro to you.