Christina, I would use a mini roller, 4 inches, with a shorter nap, 3/8 - 1/2, and try to apply just to the patched area itself without going into the non-patched areas, then apply a full coat to the wall.
The texture of the wall prior to you patching is a product of years of coats of paint and multiple variables, it's unique. If you put say five coats on the patch to increase its texture and roll that out over the non-patched areas, you are now altering the texture of the non-patched areas that surround the patch creating a "ring" around the patch, and three different textures/paint thickness on the same wall, instead of two. Light can expose the slightest variations in texture/paint thickness, especially sidelight, and apparently you have that if you can see it so clearly with a flat, either that or you're OCD.:laughing: Which could be the case.
I hate to sound technical (that's a lie) nor seem to split hairs (that is too) but you can sometimes make a bad situation worse if you're not careful or thoughtful. Can I get a witness?