Honestly, a whm shouldn't have to dps. If you hit enrage its the dps fault.

A few tips.

When charge happens only use cure 3 if its highlighted, your in the middle of the group during charge and cast it a second just after the boss cast bar begins for the charge. (use medica instead if cure 3 isn't highlighted,) this will give you time to focus on putting a stoneskin up for crit rip or avoiding a tail swipe after charge without worrying about peoples health as much.

Only use medica 2 at the end of add phases after burst and if needed during last phase, do not use it right before adds or you will pull them.

Co-ord with the other healer for eye for eye placement on both tanks during adds and slap a regen on them both so you can deal with prey. (Presence of mind is great here for quickly stoneskinning during double prey)

If everyone is topped up, don't be afraid to throw a stone skin during single preys, this may just a save the party from a SCH error. (remember to be quick, you got 6 seconds and stoneskin cast is just under 3)