Childs Party Tank Top

I’m trying to finish this tank top and I’m stuck. Not sure how far back I should go- size 2 / 50 gr ball -size 10 circular needle
[U]Left back shoulder[/U]: BO 3, p3, Knit 1 row. BO 3
[U]Right back shoulder[/U]: WS facing place sts from holder onto needle. Join yarn at neck edge. Purl across row. BO 3, K3. Purl 1 row. BO rem 3 sts.
[U]Front[/U]: Put sts from holder for front onto needles & work same as for back, through armhole shaping until piece measure 8.5".
[U]This is where I get confused[/U]. I already decreased as above right back shoulder and left back shoulder- next step- what do I do now where do the k12 sts start?
[U]Shape Neck[/U]: K 12sts. BO 10 center sts. K12 sts. Working both sides at once, dec 1 st at each neck edge every other row 3 times. Work even until armhole measures 4.5"; end after working WS row.

With the right side facing you, you start with the first 12 stitches, drop that yarn, start another ball and then bind off the center ones and finish the row.