First, does that quest give the Storm Lord spell or does it give the actual pet? (Sorry I've never quested up to level 48 storm before). If it was for the spell, congrats! Now you have a spell that will guide you to success.
If it was for the pet: Some things might have happened
1) The egg might not have hatched yet, so you won't see your stormzilla yet!
2) It might be in your bank! Whenever your backpack is full, your items to flow into your bank.