If I were = correct If I was = incorrect, but commonly used, especially colloquially If I would win = I think this is incorrect, sounds wrong to me If I won = correct

"If I was..." is very commonly heard, but textbook grammar is "If I were". So for your 2), she is singing correctly in that that is the way a lot of people speak. But it's incorrect if you are looking at grammar rules. Don't expect song lyrics in popular music to follow grammar rules. "If I would have...I would have... is sometimes heard, as in "If I would have won the lottery, I wouldn't have told my friends." But subjectively it sounds very uneducated to my ear. To say it according to the "rules" it would be "If I had won the lottery I wouldn't have told my friends." The above example is putting the hypothetical in the past. If you put situation in the present/future, it would be: "If I won the lottery I wouldn't tell my friends." You could also express is as a non-hypothetical, just a simple plan: "If I win the lottery I won't tell my friends."

Both are commonly used. Both sound normal to 99% of native English speakers. Technically, “If I were you” is better

We use both phrases, even though the grammar is not correct. It is common to hear this said in both ways. Good luck!

Hi Sedna The second conditional, used when speaking hypothetically, is structured as follows: if + past simple >> + would + infinitive. For example: If I had enough money, I would buy a house. If I met Keith Richards, I would ask for his autograph. When the verb in the if clause is 'be', it becomes 'were'. This is a peculiarity of the subjunctive mood, and is also used when we express wishes. Example: I wish I were a dog. If I were a dog, I would sleep all day. However, because people are used to saying "If I was" in the past tense, they often get this wrong. It is a very common mistake - so common that Meghan Trainor probably doesn't even realise that it's wrong! It is a similar situation with "If I would win the lottery". This structure is incorrect. The correct way to say it is "If I won the lottery", or "If I were to win the lottery". However, in many regions of the US they make the mistake of doubling conditionals, e.g. "I wish I would have been there," instead of "I wish I had been there". Just because a lot of people do it, doesn't mean it's right! I hope this helps.