Joining Rectangles on Baby Poncho?

Good Evening - I am working on a toddler poncho and have binded off the rectangles, but am not sure how to join them now. Can anyone help me? This is my second project and I’m still very very new!

Thank you!

Check out the finishing techniques on this page. Mattress stitch would be my best bet.

Thanks again Ingrid…of course the answer was right in front of my face! Have a great day