Making a square quilt into a rectangle.
 

How do I make a 48 inch square quilt top into a rectangle quilt

That is a lovely start to a gorgeous quilt. It looks like you may have to add rows and that could make the quilt look asymmetrical unless you add the rows equally above and below the centre blocks? I guess it would take using half blocks to both top and bottom, to maintain as much symmetry as possible, (if that it what you want) to lengthen it once you have decided on the width. Not sure how it would look. I would be interested to see how you do this. I have done something similar but I had to add rectangular blocks width ways to achieve the length I wanted. I will be looking out for your finished quilt. Best of luck! :)

It is just beautiful got no idea sorry, but will be watching for other answers.

I would add two more rows, then take the bottom 2 light green center blocks and another pink one on put them on the added rows. Hope this makes sense.

Pretty colors!

I would make multiple borders, making the borders on top and bottom a little wider. Your borders could be just plain strips of all your fabrics or rows of squares that look like the central area, or you could add a piano key border in the same colors making the top and bottom wider. It's such a lovely block arrangement, and the options are endless. I'm sure you will come up with something beautiful! Let us see whatever you decide!

There are any number of ways to rearrange the quarter log cabin units to make a border. Here are 2 that could be continued across the distance you have, here are 2.

very pretty......................

You can make narrower borders on the sides and wider on the top and bottom. It does work well.

You could use your background fabric for wide top and bottom borders and do an appliqué on it.