Well, it's mostly not your fault. If you're new, then they shouldn't be doing those large pulls. First of all, is the tank a decent player? Meaning, he/she dodges aoe, not just pull and take all the damage, did the tank even use defensive buffs at all? Second are the tank's gears decent? Third, did you have aoe dps classes in ur group? Aoe classes kill mobs faster thus requires less healing. Fourth, are your gears decent? They musnt do large pulls if the healer's hp is only about 4000.

Did you use regen? Do you have eye for an eye? Remember benediction.

Remember to bring x ether and the skill shroud of saints heals ur mp, about 800.

Also, be confident. You'll get the hang of it after few runs. Good luck.