Stick with it. You will wipe a couple of parties until you get the hang of it.
A word of advice, tho. Pugged DPS in the daily heroics propably outgear you and they never, ever control their threat. So you will have to develop a very thick skin.
Once you have tanked yourself to complete T9 and a couple of frost badged off-set pieces you will be a seasoned veteran of many battles.
Trust me, the pugs punish you more than you punish them.
...and begin hoarding gold. Once you've hit 80 it's time to go shopping. Having the crafted helmet, chest, bracers, shield, gun and boots sitting there waiting for you is a great incentive. With these you outgear the old content. Once you have mastered TOC/5 in normal mode it's time to seriously go to work.
Another thing that builds confidence is having good buff food and flasks handy. Since tanks have no queue time, flasking really helps. But as I said, having crafted epics sitting there, waiting for you is a great incentive. Also, since you are currently leveling up blacksmithing, the blue saronite set is AWESOME! If you are like me you should constantly scan the AH for the recipies for the ilvl245 bracers and chest. There is nothing like having your own nametag on your own gear. Those two will last you a long time.