Sounds like you're doing fine. Though I think I've seen a few places that the supposed best rotation is broken into 2 segments

Open with Blizzard III > Thunder II, Proceed to Burn

Regen: Blizzard III > Thunder II > Proceed to Burn
Burn: Fire III > Fire (Until 600 Mana) *Fire III on Firestarter Proc* > (600 Mana) Proceed to Regen

Use Thunder III on Thunderstorm procs. Use swiftcast whenever necessary to move, use scathe when you are moving and GCD isn't rolling but you can use another ability.