Yes, when you get back to 20 total Pokestops and gyms, you will get a third gym. It could even be the newly accepted Wayspot. However, if there is a Sponsored stop in the L14 S2 cell, then it will count as the third gym, and you would not get another. Here is a good article about the algorithm: https://pokemongohub.net/post/article/comprehensive-guide-s2-cells-pokemon-go/
Niantic has called it abuse in the past to try to force a certain Pokestop to become a gym. This has been discussed on the current forum, but staff has not made a comment here: From PokeStop to Gym?
We have found that a Showcase stop will not be promoted to a gym.