AceShowbiz -

After four years of dating, Nick Carter is set to wed his girlfriend, Lauren Kitt. He proposed to his fitness expert girlfriend on Wednesday, February 20, during their recent vacation on a secluded island in Florida Keys where Nick used to spend his time as a child.

"I had the ring in my pocket for two weeks," the Backstreet Boys member tells PEOPLE. "I was like, 'I don't want it anymore!' It was driving me insane. I just wanted to get it out of my hands and on to hers."

Nick took Lauren to the secluded island by a boat. "My boat was in such bad condition because I hadn't used it for, like, six years. It took me five days literally on my hands and knees, scraping up my body (to fix it)," Nick says. "The engine wasn't complete yet but we still decided to go out."

Once they arrived at the island, Nick dropped to one knee and presented his girlfriend with a seven-carat diamond ring from XIV KARATS. "She said, 'Yes,' and I'm, like, 'I don't know what to do,' " Nick continues.

"I wasn't expecting it. It just felt very surreal," Lauren says. "We both are just so happy in love right now and on cloud nine."

While the couple has planned the marriage, they haven't set the date. As a member of Backstreet Boys, Nick is going to be busy due to working on their new album. "It's not up to us. It's up to the schedule. We're just excited and looking forward to the next chapter of our lives," Lauren adds.