Former Manchester United, Real Madrid and England star Beckham, a co-owner of the new team, had dreamt of launching an MLS team after playing for LA Galaxy, but the 44-year-old was still surprised by the difficulties.
"It has been a long journey," Beckham told a news conference on Wednesday, via the BBC.
"There was never a moment when I said I would walk away but there were moments when I thought this might not happen.
"I have always loved a challenge. I didn't realise how big a challenge this was going to be, even down to putting tiles in the showers."
Nashville will also enter MLS in 2020 and recent expansion teams LAFC and Atlanta United have made a huge impact.
Atlanta were MLS Cup champions in 2018 and have made the play-offs in each of their first three seasons, while LAFC reached the postseason in their first two campaigns.
"Kicking the first ball this weekend is going to be success for me," said Beckham, who teamed up with Jorge Mas in 2017.
"But I didn't want to be in partnership with someone who was in it for a vanity project. I want my children to be able to say, 'My dad built this club'."