Don't worry - you are more than ready for your first dungeon. (Which BTW isn't a "raid" - that usually means a dungeon designed for more than 4 players.)

Sastasha is a quite easy dungeon. Literally a training dungeon - it is after all the very first dungeon people will run in this game.

If you have read up on the dungeon, understand your class and know more-or-less what to do - then you are better prepared than most people are on their first run.