I get 24 as a count also, since for every st you're increasing 1, so in effect doubling your original 12. The only way I can see getting 18 is if it's supposed to be K2, M1 around the round, or K1, P1, M1, or something similar.
Maknitter2  when you're counting between each knit and got 21, I think you forgot to include the M1 between the knit st at each end of the needles. That would be 3 more and would give you 24.
___________
