I think every new tank has been through that at some stage. I still don't do levelling roulette as I hate tanking the old dungeons (I came to the game late so most I've only run once,and even then as my first job, DRG).

However, HW just made me say stuff it and jump in feet first. You will make mistakes, but the vast majority of people are OK with that. I've certainly had a few howlers when levelling (PLD was entirely through hunts and dungeons) but haven't so far encountered anyone especially hostile. If you have a fc, see if someone there will level with you, perhaps as healer as you'll then at least have one friendly face in each dungeon.