There is also the element of hearing the tune as you sing it, not just recognising the tune you are trying to sing (if you see what I mean). This is why so many unacompanied folkies sing with a finger in the ear. Even though everyone thinks it looks risible, it helps you hear the sound that you are actually producing, and thus makes it more likely that you will hit the right note.

I have experimented taping myself singing with and without a finger in the ear (in private) and there is definitely a difference. I always have a finger in my ear on Paltalk, although anyone who's heard me would probably claim it is no improvement.

What Wesley says about singing in the car to exercise the vocal muscles is very true. Also try taping and listening to what you sing, what you hear as you are singing it is very different from what everyone else hears.

Also be uninhibited, practice alone if necessary, and don't be afraid of making a fool of yourself.

A song well sung is one of the great joys of the world, it's worth persevering.