"I am going to be extremely nervous," the busy star, 26, tells CMT Insider about performing "The Star-Spangled Banner" at the big game between the New Orleans Saints and Indianapolis Colts. "If I look like I am about to get sick on the field, I may at any moment during that song."
Underwood (no stranger to football, having dated Dallas Cowboy Tony Romo) also admits she will be playing favorites on game day – but refuses to share whom she's rooting for. "I don't want the other team's fans to hate me forever," she explains. "I am just there to have fun."
The singer is slightly more forthcoming about her plans to wed hockey star Mike Fisher, 29, of the Ottawa Senators. The couple have been working on their guest list – "the more the merrier," she says – and Underwood reveals that she's had a bit of trouble securing her engagement bauble.
"I've had to have it sized like twice because I have the smallest fingers in the universe apparently," she says.
The rest of CMT's interview with Underwood will air on CMT Insider this Saturday, Feb. 6 at 1:30 p.m. ET/PT.