Usually when there's a wipe and you feel that you are a decent healer, it's other people not doing their jobs.

A good example is Titan (hard and extreme). If somebody eats a plume, they're dead. You can't do nothing about that.
If somebody eats a landslide, they are probably dead. You can't doing nothing about that either.

A lot of time, there are things that happen that aren't controlled by a healer but by how everyone else in the party plays.
DPS/Tank eat unnecessary things, more healing from you or you'll have to rez them.
Tank doesn't tank adds or dps don't kill them, you'll get hate (which usually isn't your fault, healing is a lot hate if no one has hate)

Just pick your head up and brush it off. First time I did Ifrit extreme, I thought I was a crappy healer too. Then I realized what was going wrong
and what I couldn't control. Picked up my pieces, and moved on and got my win that same night. Just think positive :3