Need help making a fireball/fireblast macro

As an arcane mage the following macro worked perfectly:
#showtooltip Arcane Blast
/script UIErrorsFrame:Hide()
/cast Presence of Mind
/cast Lifeblood
/cast Mana Gem
/script UIErrorsFrame:Clear()
/script UIErrorsFrame:Show()
/cast Arcane Blast

But now i'm trying a fire mage and want to use this one: It never casts the fireball in the end. Any help?
#showtooltip Fireball
/script UIErrorsFrame:Hide()
/cast Lifeblood
/cast Fire blast
/script UIErrorsFrame:Clear()
/script UIErrorsFrame:Show()
/cast Fireball

Because Fire Blast generates a GCD which makes it impossible to use Fireball straight afterwards.