In general, very superficial scars, such as those left by a blister, heal extremely well and leave no permanent mark or scar. The top layer of your skin (the layer involved with most simple blisters) is composed of cells that are dead already, and so the cells underneath simply take their place after the blister flakes off. Because their is no structural damage beneath, the cells from the sides don't have to grow in to replace them. This ingrowth and the collagen that is needed to make it happen is what makes the new skin look different from the old when you have a scar, and explains why blisters usually don't scar. It is important to note, however, that this depends on the size and depth of the blister, as well as how much trauma the area continues to experience. If the area is constantly being bothered, your skin will respond by eventually forming a callous. For the most part, this thickening of your skin is reversible with hydration and protection, but it can also be unsightly for a time. As you mention that the area is still puffy and discolored, it is important to make sure it is not infected, which could leave a permanent scar by affecting more tissue. Please speak with your doctor
about your concerns.