"I just try to be in control of what I can do and not worry about what the others are doing," said Kropp, who clocked a personal-best mark of 2 minutes 27.61 seconds to place fourth overall in the event at Stanford University's Avery Aquatic Center. "I'm just going out there trying to get the fastest time that I can.
"You go out there and do the best you can. I started off well and did well during the back half of the race."
Kropp, a member of the Rattler Swim Club, will fly to China today to prepare for the prestigious competition.
On Saturday night, she eclipsed her previous best mark of 2:27.63, set in 2010 at the national championships at William Woollett Jr. Aquatic Center in Irvine.
The reigning News-Press Female Athlete of the Year went into Saturday's race brimming with confidence after she placed third earlier Saturday in the prelims in 2:28.65.
"I wanted to make the national team and it's anybody's race going in," said Kropp, who won an Ivy League title in the 100 breaststroke in February. "You know you are going up against other great swimmers, but I had to stay focused."
Micah Lawrence won the event in 2:27.06, followed by Haley Spencer (2:27.09) and Michelle McKeehan (2:27.57).
Kropp said she'll take the same race approach in China as she did Saturday.
"In hasn't quite sunk in yet, but it's going to be great to be able to represent the United States," said Kropp, who clocked 1:09.82 to tie for 17th in the 100 breaststroke at the national championships. "These are going to be high-level [races].
"Once I get there, the energy surrounding the race will help me out. We'll see what happens."
La Cañada High senior Katy Campbell, the reigning All-Area Girls' Swimmer of the Year, clocked 8:48.99 to finish 27th in the 800 freestyle on Saturday night. Campbell, who swims for Swim Pasadena, won a CIF championship in the 500 freestyle for the third straight season before winning a pair of championships at the CIF Masters Meet.