The Northampton star, who is the only Brit to win a medal at the World Championships in Montreal so far, recorded the quickest split of her team-mates, one minute 58.26seconds, as Britain finished fourth in the 4x200m freestyle final behind America, Australia and China.
Britain looked set to win only their second medal on in the relay until China's last leg swimmer Yu Yang chased down Rebecca Cooke to claim the last podium finish.
America recorded a World Championship record time of 7:53.70 as they held off a strong challenge from the Australian quartet, while Britain recorded a combined time of 7:59.04 back in fourth place.
"I know we will go from strength to strength and I think we can catch both the Australians and the Americans," said McClatchey. "We did our best in the relay and I think we all produced a magnificent job.
"I was so proud of everyone in the squad and I feel privileged to have swum in the same team as Rebecca Cooke, Joanne Jackson and Melanie Marshall. We can still get stronger.
"Everything is towards Beijing so hopefully if I prepare well and compete well it will stand me in good stead.
"If I don't this is a learning curve and I will put it down to experience. I really want to swim in Beijing because that is the main focus for me and the relay."
Jackson added: "I have learned a lot from this experience and it can only make us stronger in the future."
Portsmouth's Katy Sexton will make her debut at the World Championships today in the 200m backstroke.
Sexton, 23, will race in the fifth heat, with her biggest threat likely to be Reiko Nakamura, who is in heat four. The Japanese swimmer is the favourite for gold after recording the fastest time at the distance earlier in the year of 2:10.22.
Glasgow's Cooke will get her second and last chance to win an individual medal. Cooke, who failed to make the podium in the women's 1500m freestyle earlier this week, finishing in seventh, will go up against France's Laure Manaudou in the 800m freestyle. Meanwhile, Michael Phelps, fresh from his gold medal performance in last night's 200m individual medley final, will attempt to qualify for the semi-finals of the 100m butterfly.