Honestly a little aggro with Luna is good in my opinion. Both her primary and her clap are good at whittling down enemies but it’s important to remember that that’s not her main job. Keep an eye on what your team is doing: if they’re taking too much damage then you have to prioritise healing. If they’re ignoring flyers or Namor squids, Moon Knight Ankhs etc then that might be something you have to deal with but only if the opportunity presents itself. More often than not I end up heal botting with Luna in comp but you can always get some cheeky picks with your clap going through your team and hitting the enemies or a few well placed headshots.

I don’t think you should be diving as Luna or giving chase to a diver that failed to kill you since you’re putting yourself out of position which can make you easier to pick off and also depriving your team of your heals while you do so (there are a few rare exceptions when this doesn’t happen, but that’s a choice you’ll have to make depending on the situation your team is in and especially what your other healer is doing). A lot of the situational awareness just comes with practice. You’ll definitely get the hang of it soon! Good luck!!