First time poster

The other week I purchased a pair of Mammut Sierra GTX boots (Mens). I tried them on in the store with a pair of Coolmax socks (medium thickness), and they were a perfect fit. For my first hike I overdid it a little, 22km later and I had blisters. I found that my boots that fit perfectly in the store now seemed too large.
I went for a hike again yesterday (10km) with a thick pair of socks. With the boots as tight as I could get them they still seemed a little roomy. At the lunch stop I though I'd try on the coolmax socks AND the thick socks. Surprisingly they both sit and the boots seemed quite comfy. Finished the hike with no blisters.
What I'm curious on, is have my boots stretched? Do you think they might be too big?
Cheers