Oh boy... You're lucky this is FFXIV cuz anywhere else, this would of been an open mic night roasting you for playing like this AFTER FIFTY LEVELS. Now as a fellow tank, I'm gonna be real with you. That kind of play is not acceptable. Like others have said, shield lob once then spam flash. Shield lob is okay to use if a mob got away from the pack and it slapping another party member around. You usually wanna go Shield Lob then spam flash 2 or 3 times and use Circle of Scorn. Spamming Total Eclipse ain't bad if you're in Shield Oath either.

After you got their attention, feel free to just use Rage of Halone combo until you get Goring Blade and Royal Authority. Tanking is a tough job and I commend you picking it up but for the sake of everyone who will party with you in the future, read the tooltips of your skills man!