Duuuuude! That was my first G rank solo quest! I didn't die surprisingly, but i BARELY f***in made it! I used up all my potions, flashbombs, traps, and urthang! AND i when all that was gone i had only taking out like 50% of the 2nd Hypnocatrices life! Then i got scared and fought it the smart way, hit and run, exchanging attacks but dodging all the hits and getting out of its way.
I also used a greatsword.
So just keep trying and play smart.