ARVADA — If Barrett Kerrigan had concerns ahead of his final individual prep swim, he maintained one heck of a poker face. The Cheyenne Mountain senior entered the 500 freestyle seeded fourth, but Kerrigan exited the pool Saturday at Arvada Aquatics Center with his third consecutive championship.  Kerrigan clocked in at 4 minutes, 36.79 seconds in the 500 to cap his career with another title in the race and, for the first time, earned the 200 freestyle title. Kerrigan finished first in the 200 with a time of 1:40.46 for the double title at the 4A state boys’ swimming and diving championships.  “Sophomore and junior year I won the 500 but this year I set my sights on winning both of my individual events,” Kerrigan said. After Friday’s prelims, that opportunity appeared to be in jeopardy. Kerrigan clocked a 4:46:03 in the 500, which was more than 10 seconds slower than his seed time of 4:36.79.…