The Rio Olympic bronze medallist has been analysing her run up, after pulling out of a number of jumps in qualifying.
"It's just the rustiness that's happening at the moment," she said. "Maybe I don't have the confidence in it because I've had to rush things to be competition ready."
McCartney's vaulting off a different run up that saw her burst onto the world scene last year in Rio, reverting back to the run up that saw her jump 4.82 metres in Auckland at the beginning of the year.
Filled with nervous laughter after the qualifying stages, McCartney has calmed and ready to compete for her first World Championships medal.
"Now that im in the top 12, things are a lot less stressful. Every place you get on top of that is a bonus as you've already done the hard work."
The bright lights of London's Olympic Stadium has done little to alter the relaxed attitude of New Zealand shot putter Tom Walsh.
He can become New Zealand's first male medallist at a world champs, but planned to take things a lot easier than McCartney after throwing a season's best 22.14 metres in qualifying.
"Sit back, relax. I've just caught up on the new Game Of Thrones and have watched the three episodes, so I'm going to have to find something else to watch which is sad."
Jacko Gill will also be flying the New Zealand flag in the final, producing his best throw in seven months with his first effort in qualifying.
The 20.96m throw has surged Gill with confidence that he can produce something special.
"I think there's a really good chance of doing something pretty good in the final and I hope I can do it for the country".
The major obstacle in Tom Walsh's way of gold is American Ryan Crouser.
Despite the Rio champion throwing 20.90 metres in qualifying, his season's best is 22.65 metres.
The American is hell-bent on adding a world champs gold to his Olympics gold.
"Tom and I are good friends," Crouser said. "His [effort in qualifying] is a sign that there'll be some big heaves. Tom's a good thrower so it wasn't a big surprise, it just motivates me to go out there and do well... My performance in qualifying was below my usual standards."
Eliza McCartney's final begins at 6am, while Tom Walsh and Jacko Gill are in action from 7:35am.
-Charlie Bristow is in London thanks to Air New Zealand