Trying out keys, don't wanna drag anyone down.

Heyo. I've been jamming shaman for many years as Enhance and Resto, primarily just raiding with my guild and doing delves and world content. I wanted to try to get into keys to get myth track loot thanks to voidcores, as my guild is just aotc non-myth raiders and a few key gamers. However, although I can 2 heal heroic Lura while doing crystals in a 15 man raid, I'm terrified of being a "shit heals" in keys. I'm ilvl 278 currently and just getting my feet wet in 4s and 5s currently. Any tips for overcoming the fear of pushing to 10s and above?