Looks like you readers have beat me to the punch here! (pesky sleep interfering)

@Luotian I can only echo what's already been said, it's darn good advice. Take what Eberron said to heart here. While we're capable healers there's no sense in giving yourself an handicap. Making sure you have gems, even if they are green quality, and enchants will give you a huge boost in your stats and make your job healing that much easier.

Icepyro has some very good points. Keeping Riptide on three targets is fine for raiding, but in a dungeon it's not as necessary. Judge your heals. Chain Heal, as awesome as it is, is not always the right answer for the job. If people are too spread out you have to rely on your other tools. Don't be discouraged either, Cata heroic are rough on healers that just reach them. There's no shame in that. If you find it's too hard, don't be afraid to hit normals and farm some gear. Also rep rewards are also available and can help you gear up as well. Remember it's a game of leapfrog when it comes to gear. Quest>rep/dungeon>heroic>raid

Here's a list of rep gear http://wow.joystiq.com/2010/12/14/totem-talk-restoration-shaman-guide-to-cataclysm-reputation-gea/

Should help you find pieces to fill the gaps.

Also keep in mind what murmaiderxx said. If you're in a group and peopel are not doing what they are supposed to, especially with a new or undergeared healer, things will unravel quickly.

Ultimately keep trying, fill in your gems, get enchants, farm up some rep gear and make sure you're using the right tool for the right job. Keep trying, keep practicing until it feels right to you.