Scratched the paint off the wall. How to proceed?
There are a couple things to consider.  First, with regards to color, is how old the paint job is.  After the initial cure (during which the color usually darkens slightly), paint will yellow over time, and it also accumulates dirt and debris which further affect its color.  Smoking in the house speeds this up.   What this means is that older paint is harder to match generally.  When it comes to color matching, keep this in mind and if possible, let the store doing the color matching (using the chips you saved) know about the age as they might suggest slightly altering the color.  Working in your favor is the size of the damage - something this small won't be as noticeable as say a large 12"x12" patch.

Next up is texture - it sounds like your paint was applied with a roller originally, so you should be sure to use a roller on your patch.  If you use a brush then the texture difference will be more noticeable.

The above two techniques should help you blend the patch, though it will still be noticeable to some degree.  If you are a perfectionist then the only "right" way to do it is just re-paint the entire wall/section.