How do I finish the back of this top?

I just recently started on a commission for sakura from le sserafim’s top for a friend and I’ve finished the ribbing and the front part of the top. But I unfortunately don’t know how to do the back of the top. My biggest problem is the bust is supposed to measure 33 inches but the ribbed part of the top only measures 28 inches since it’s supposed to be under the bust. I don’t know how to attach or crochet the back part which is supposed to make up 33 inches on to something that is 28 inches. I was planning on continuing the back and just doing an increase stitch after each row, but the sides of the ribbed part are lose since I chained three and skipped one stitch at the start of each row. For the front side, I attached the front panel by doing two slip stitches in the “big holes” and one in the “little holes” and it created this little join which covered the big holes nicely and I wanted to incorporate that on the backside too. I also have no idea how to attach the front panel to the back side 😭. I followed the star girl top tutorial online and she did a mesh back for the top but my friend wanted a solid back. I was just going to make the back side and pray that it’ll attach correctly but I don’t want anything to go wrong. Please help!! (I’m using a 4.5 mm hook if that’s relevant)