Problem knitting 6.mo sweater

I’m in the middle of my first time knitting a sweater and the pattern has confused me. First, I knit the back in stockinette until it was a big rectangle, pretty simple. Then the pattern gives me instructions for “Shoulders and Collar.”
CO 12 sts, and K next 30 sts. BO remaining stitches.
Slide remaining stitches from back to a stitch holder for collar.

So I cast off 12 stitches, then I knitting 30. However, there weren’t enough stitches so I had to cast on stitches to the end. Then I bound off the remaining stitches, which left me with a long sticking out line of stitches and the other half bound off.

Next, after making another rectangle for the front, the pattern says to make the collar by “putting the collar stitches from front and back on needles. Joinn into a round and K for 2 in. BO all stitches.”
I think I did something wrong to my back piece because it doesn’t seem like I should really join the two pieces together.

Please help if you can! Thanks.

Could you please tell us the pattern name and post a link if possible. Don’t post the pattern here just the link.

220 Superwash Frog Sweater & Hat

From what you’re posting, you should have had 54 stitches on the needle, 54-12= 42, k the next 30 would’ve left you with 12 stitches. So something tells me that you didn’t have enough stitches to begin with if you had to cast on more.

I’m sorry, I made a mistake in my original post. When it said CO 12, I cast on 12, not cast off. Then I knitted 30, which included the 12 I just cast on and 18 of my original stitches. Then I bound off the last 36 stitches left.

Did you start with 54sts as Rorshach mentioned in his post?
According to the directions, you won’t cast on any sts here, just bind off 12sts at each side of the center 30sts.
12 bound off–30sts on holder–12 bound off

How many sts did you have on the needle before you began the cast offs?

hello,

So for your back you should have had 54 stitches, when you get to the collar bind of twelve stitches, knit 30 then bind off another 12 this should leave you with 30 stitches on your needle to put onto a stitch holder