The World Wildlife Fund has made this error.
And let's not even get started on Bieber.
See the pattern? "If I was" is just not correct.
The correct phrasing in these cases utilizes the subjunctive verb form, making it "If I were..."
As the Oxford Dictionary defines it, the subjunctive is "relating to or denoting a mood of verbs expressing what is imagined or wished or possible."
It's often used, therefore, in cases where the speaker is expressing a desire or making reference to an event that might not actually happen.
Want an example of someone who gets it right? Look no further than Beyoncé.
So if I were you, I'd be sure to start using the subjunctive today if you don't already!