So not even 90 yet. You need to learn to do your job first and foremost. These early, easy zones are your best chance to learn how to do it. Your job is to heal and cure your group. You are a Priest, and those tasks are always job 1. Secondly you debuff the mob. If you still have time after that, throw what DPS you can at it.
You weren't brought to the group because you could DPS. I promise. You were brought to keep the other players alive and able to do their jobs without impairment.
Just because a given effect isn't outright killing your group, does not in any way mean it doesn't need to be cured. It could easily be a Stifle, and you as a Steadfast Cleric, would never know. It could be a tiny DoT that has an interrupt component which keeps screwing with the other casters in your group. It could be a root that prevents other members of your group from moving as they need to. Whatever it is, you have no excuse for not getting it off them.
You are a Priest that can DPS some, not a DPS that can heal some.