Sentences

The first and second are correct as is.

The third one is tricky because it begins with "if" like number 2 which usually indicates the subjunctive mood. But the context might make "was" the correct verb. Let's say the discussion concerns an upcoming football match and the speaker is one of the star players. In that case, the speaker's presence at the game could truly make a difference and "If I was" is a conditional phrase, making the use of "was" correct.