The only notes that are technically "out of scale" are the minor second (+1 semitone) and the Augmented 4th/Diminished 5th (+6 semitones), but there are even times when those notes could sound good!

If you're really worried, just think about if the vocals are in major or minor and if your song is in major or minor, and avoid certain transpositions that would fall out that (avoid +3 when major, +4 when minor, etc) and break that rule if it's not quite sounding right. Like eidolon said, the most important part is to experiment and see what sounds good to you!