My mistake. I misunderstood what you had originally said and apologize if my tone came across as accusatory.
This combined with your other updates makes me think it's most likely both you and the tank were undergeared coupled with inadequate CD management on the tank's part. If you use everything before Cure II spam then there's really not much else that can be expected of you. I'd still recommend buying Augmented Scaevan for poetics in Rhalgr's Reach. Healing margins on large pulls can be incredibly tight if the pull goes long (low party dps) or if the tank is undergeared. Having an extra 20% healing output can make all the difference.
Edit: Another thing that might help is to glue yourself to the tank while they're pulling. If they sprint, you sprint. If they start moving ahead, you start moving ahead. In the best case you're in position to Holy as soon as they stop. If they take massive damage while pulling you can stop to heal without falling behind. If the tank is using light or no CDs while waiting for your first Holy they can take a ton of damage if you're three or four seconds behind them.