Wipe Away Scratches and Recoat the Surface
You can buff out fine scratches using very fine (0000) steel wool saturated with clear Danish oil. (You can also use ultra-fine automotive rubbing compound.) The process shown here only works for scratches in the finish itself, not scratches that are all the way into the stain or the wood.
Pour a generous amount of clear or neutral Danish oil onto a very fine steel wool pad. Rub the surface with the oil-saturated pad using your flat hand. Rub with the grain, never against it or at an angle to it. Continue rubbing until you remove enough of the clear surface finish to eliminate the scratches, but be careful not to remove any of the stain below the clear finish. Rub not only the scratched area but also the area around it in gradually decreasing amounts. Be careful to rub edges or corners excessively; they wear through quickly.
Wipe away all the Danish oil with rags or paper towels, then thoroughly clean the entire surface with mineral spirits several times to make sure all the oil is removed. If any oil remains, the lacquer won't adhere. Allow the surface to dry overnight before applying lacquer.
Spray the entire surface with clear lacquer. Move the spray can in one continuous, straight stroke, allowing the spray to extend beyond the edges in all directions. Wipe the nozzle with a rag after each stroke to prevent drips. Move with the grain, and make sure the angle of the spray remains the same all the way across. Keep the spray aimed away from other surfaces that you don't want coated, or mask them with newspaper.
CAUTION: Rags and steel wool saturated with Danish oil can spontaneously combust if left bunched up. Dry them outdoors, spread out loosely, when the oil has dried, you can safely throw the rags and steel wool in the trash.