Hate to be the one to bust your bubble but technically you have to go back and amend the 2015 return to show the sale of the home on the 5405 form for that year. Then you would amend the 16, 17, 18, 19 and 20 tax returns to get back the $500 per year that you paid in correctly. The really sad news is you can't get refunds for 15, 16 or 17 at this late date and you can only get the 2018 if you file the amendment before April 15th of this year so get cracking.
