Quilted Twins has a treasure-trove of free patterns for scrap quilts. They have many for 2.5" squares. Some of the quilts use 2" squares, but 2.5 can be used instead. Here is the link:
https://www.quiltedtwins.com/free-patterns-layout-2 (scroll down to the patterns).
My favorites are Swinging Checkerboards, Circle the 9's, Scrappy Rail Fence, Diamonds in the Rough, Circling the Wagons, and Granny's Selfies. I've made several of these that were designed for 2" squares using my 2.5" squares. They came out great!