So, I've always kind of considered myself a C+ (if that) singer, and I don't really have any way of funding this ability, though I wish I could. I'm posting up a song that is pretty much how I sing all the time, so please... be as harsh as you need to be tell me I suck hard if you need to, just be constructive and give me some tips on improvements and what I'm doing wrong.
I really don't think your a bad singer. That being said, I don't think you can compete with the likes of Stevie Wonder but not many people can. I would give you a B+. There is room for improvement however. I think more practice is the answer to that. Do you practice singing scales or chords? You could play a chord on your guitar and sing the notes of that chord and it will help improve your voice. This is also how pop songs are made, just singing melodies with notes of the chords your playing whether it be a piano or a guitar. You shouldn't be so hard on yourself, you just need to improve a little, thats all.