I would say that you are on the right track with the guitar. Use a piano (or your guitar) and go through some scales. You were hitting most notes but it seemed as if when you first hit the note, it would be somewhat off but then as you sang the note longer, you would correct yourself. I definitely recommend just sitting down and plucking out single notes on your guitar and singing along and eventually, you will train your ear and voice to immediately hit the note. Keep up the good work!