Can I use "whether" instead of "if" here?
Yes, you can use "whether" instead of "if" here. In informal speaking, "whether" and "if" are often used interchangeably. However, "if" is more common and informal while "whether" is a little bit more formal. If a sentence is conditional and only presents one option, it is usually okay to use "whether" and "if" interchangeably. However, if a conditional sentence presents two alternatives, you should always use "whether". Ex: I don't know if she's going to the party. Ex: He didn't say whether or not he is interested in the job. Ex: Whether rain or shine, we will still have the soccer game.