formatting external drives

Stupid mistake! Whilst trying to format a flash drive in MS Dos, I stupidly clicked on MY 2 TB external hard drive that carries all my pictures that are in Mac OS Extended (Journaled). Within 2 seconds I realised my mistake and cancelled the action and then ejected my hard drive and switched my computer off.

Now I have rebooted and attached my hard drive which has now come up in MS Dos, showing there is plenty of data still on it but I cannot view it!

How do I change my hard drive back to Mac Os Extended without losing the data on it and thereby allowing me to view my pictures again??

Please help!