Eilidh Child feels she "threw a medal away" after finishing sixth in the women's 400m hurdles final at the World Athletics Championships in Beijing.
Great Britain's Child ran a time of 54.78 seconds, some way off her 54.22 personal best.
"I felt I could have got a medal if I'd executed my race a bit better; I was a bit messy over the hurdles," Child told BBC Sport.
"I just feel like I've let myself down a little bit."
Zuzana Hejnova of the Czech Republic; won gold with a 53.50 run, ahead of American duo Shamier Little and Cassandra Tate.
"The good thing is now that I'm disappointed to be sixth in the world," Child continued.
"When I was fifth in Moscow [at the 2013 World Championships] I was absolutely delighted just to be there, but now I'm annoyed I'm not up with these girls.
"I'll take this motivation into the winter and hopefully I can do something at the Olympics next year."