I had scratches on my face that have healed in a week, nowi have a red mark under skin that wont fade what can i do and how long will it take to fade?

Have patience: At the age of 19 you may have skin that is at its most reactive stage in life. Such hyper-reactivity usually settles with age. The fact that the scratches are only a week old bodes well for their ultimate resolution. At this point the topical application of over-the-counter agents such as vitamin e oil or mederma may be helpful. In time the scratches likely will improve, though it may take months.