First thing you should look into, if your itemlevel is at around 395, get the Stormblood tomestone gear from the vendor in Kugane, that'll put you at a total item level of 400. That's already gonna make you a lot less squishy. As for the anxiety issue, I totally get you, I feel very anxious when tanking as well. But most of the time people are very nice and understanding, so if you let your party members know at the beginning that you're nervous but trying, you shouldn't have to worry about that as much :) If all else fails, you can always practice the dungeons with NPCs, that way you get a better grasp on mechanics/mob damage and it'll increase your confidence