The Citizens remain favourites to appear at Wembley after coming from behind to beat their Championship opponents at the Etihad Stadium on Tuesday night.
"It's a semi-final, I don't care what the competition is, it's a semi-final so it's not easy to reach and we knew they would be difficult opponents," Guardiola told BBC Sport.
"We created a lot of chances and that's why we win in the end, but today we knew we are not going to finish our job - that will have to happen away in Bristol when we travel there.
"They were really good, so we tried so hard, all the players tried and we're really happy."
The return leg takes place at Ashton Gate on Tuesday, January 23.