Buy some fish material, looks like you need some color.
Cut strips of fabric and put between the blocks, any block of a different size add a strip to enlarge, the blocks will need to match at some point to sew them together.
After getting your horizontal rows matched/together, then start the verticaql rows, do the same thing. Adding strips of fabric, adding sashing to enlarge small blocks.
Add narrow strips, wider strips, whatever to get the blocks lined up so you can sew the rows together.