To cap off the learning the top 3 strings, here's Happy Birthday. By now, you've made great progress if you've sequentially worked through these, ingraining the note names of the strings into your "mind's eye". Following this, you'll move onto the 4th string; the D string.
Here's your fretboard/note cheat sheet to figure your way through the song.
Alright now you're ready to dive into the deep end. Best of luck working through the classic, Happy Birthday, which according to Guiness World Records is the most recognizable song in English! As a reminder, you can always review the section on music notation, to brush up on knowing any of these symbols.