Sorry if i sound rude, as im not a very good player myself.
But dying to a murderous megamoth as sorcerer seems unneccesary, just keep your distance and fire away.
It seems you are trying too hard to get top rewards, take too much risks.
Im slowly getting better myseld at pressing the nexus button. Some rules i try to live by:
a) Am i confused by whats happening and is there high danger: press nexus, then wonder whats going on, not the other way around
b) is my hp bar orange: press nexus
c) is boss almost dead, and you are in a bad shape, dont try to outlast the boss, the loss is far greater than the gain.
Dont do dungeons you are really bad at, unless you are ok with dying: so dont start O3 at 12k fame if you are not good at it and want a white star, get to 15k then try o3 if you want it. Just stay patient.
Good luck !