Don't worry, it's overwhelming when you are healing in pvp for the 1st time, I felt the same.
I would suggest you to try to practice in 8v8 parties where you have another healer to help you, where you can discover the map as many of players here are for now newcomers. 4v4 is mostly filled with veteran players premade (not always but mostly). They are prepared, they know their jobs and have a nice synergy.
In 8v8 you can only tag as a party of 2 players so you won't get stomped by premades. Practice is the main advice i can give you. Practice and don't panic. It happens and it's not only your fault.
Sometimes a party member focused by the entire enemy team will die anyway, even if you use all of you CD to save them.
Read your pvp skills, they can be really useful. Pvp healing is nothing alike pve healing. It's just an habit, don't wait for you teammates to lose HP to start casting a heal, don't only spam Aspected Benefic, use your lightspeed and use Benefic II if your mate is getting rekt.
Btw i'm healing in pvp as a whm but some stuff are in common, i just hope i'm not telling you BS since i rarely play my ast.