Are you wet-sanding between coats? Ideally, it's best to do 2 or 3 coats, let it dry a couple of days then sand (carefully) with 400-grit wet-or-dry soaked in water and washing-up liquid.
Then wipe it clean, do a couple more coats and repeat the process as many times as you have patience for! As you build up the coats, your sanding lines will gradually fill with finish and disappear.
After you've built up at least 10-12 coats this way, let the final coat dry for at least 2 weeks, then wet-sand with 800-grit, then 1000, then 1200 etc - the finest you can get hold of (I have up to 2500). Then polish the whole thing with T-Cut.