Sounds like you're doing nothing wrong mate. Its the rest of the party's fault. I found healing through HK 47 extremely tough on a well geared operative. It takes all the attention you can muster and i still needed a bit of help healing the dps from a sorcerer. Its a tough fight if the dps are crap and its not a fight the healer can sit and mash one button all the way through.
Also, i think you can interupt his snipe so get one in here and there and have the dps do the same of they can. They need to burn the adds down asap, which shouldnt take too long to manage.