If I Was, If It Was
The lines are smudged in everyday speech, and this is the phrase most likely to be used, but it is only correct in certain references. “Was” is used in situations where the statement might once have been or could be a reality. This verb mood is called “indicative”. These subtle differences once enabled a speaker to “indicate” something without using more words to spell it out.
“If I was home, I would be sitting on the couch eating chips.”
The speaker indicates with subtlety that he intends to go home, and potato chips will be involved.