Boyle thought she made a mistake by trying to mark herself against the big guns in the middle of the pool, rather than concentrating on her own race.
The final was won by France's Camille Muffat, who won in Olympic record time. American Allison Schmitt was second, while Rebecca Adlington picked up the hosts' first medal in the pool, finishing third.
Boyle, a graduate of the University of California, Berkeley, will now focus on the 800m.
She remains the only New Zealand swimmer to make a final, after Gareth Kean finished eighth in his semifinal in the 100m backstroke, despite turning for home in first. His time of 54s flat was half a second off his personal best.
Earlier, American Dana Vollmer, a former training partner of Boyle's at Berkeley, set the meet's second world record in winning the 100m freestyle. Vollmer posted 55.98s, beating the old mark by .08s.
She was followed by South African Cameron van der Burgh in the 100m breaststroke. He shaved .12s off Brenton Rickards' mark of 58.58s, set at Rome three years ago.
Frenchman Yannick Agnel turned in a blistering final leg to overhaul American star Ryan Lochte to secure the 4 x 100m freestyle title over the world and Olymipic champions.