What's done is done, and congratulations, but given that the following dot coms are for sale:
sellprivatejet is for sale for $23,800.
buyselljet $10,000.
weselljet $35,000.
jetdeal $41,600.,
and also if you look there isn't really any "buymy" short domain name being offered for much under a few grand, and the "sellmy" are mostly all being offered over a couple grand,
$500. seems really low.
I mean, you may find on the other side too (the low side), for example from namebio
jetdeals dot com sold for $511. 8/4/2017 at GDaddy, which would make the jetdeal $41.6K listing seem very high, but keywords buy or sell, and jet are apparently asking for a lot right now.
Maybe you did well, or maybe you just crashed the comparables market by selling your Beverly Hills mansion at Watts prices.