Compounds A and B will give your resin a glasslike finish that you cannot get from sanding alone.
Before using the compounds, sand the rough edges of your cast resin piece with progressive grits of wet/dry sanding papers. Start with 100 which is a very coarse grit (use only if needed, where heavier sanding is required), then move progressively through the following grits in water: 220, 320 or 360, 400, 600, 800, 1000, 1200 and 1500. As you move to the finer grits, less sanding time is required for each. The finer grits may only require a few passes over the area to finish. The resin will feel pretty smooth, but still will have a "foggy" appearance that can only be removed through buffing and polishing. Use a SLOW speed (1000-1500 rpm) on a variable speed bench lathe in conjunction with muslin buffing wheels to which compounds have been applied (Compound A followed by B) to give your resin a professional finish.