The third daughter of Jim Bob, 49 and Michelle, 47, one of 19 kids in TLC's hit reality show 19 Kids & Counting that starts its new season Sept. 2 at 9 p.m., had more than one surprise on Aug. 14 – the day boyfriend Ben asked her to marry him.
"A few days before, he had given me a rose and asked me out on a date for the next night," Jessa, 21, tells PEOPLE. "But that night we had gone out with his parents and my parents. It was a surprise because I didn't know his parents were in town. But that night he gave me a box."
Inside the box was an iPad with a video Ben, 19, had recorded, telling her, "This is the first clue to the rest of your life."
"I had done a few things to throw her off track," Seewald tells PEOPLE. "Jessa is really good at figuring things out and I wanted to surprise her."
Jessa's journey to "yes" started with a plane ride with her brother John-David, who took her from Springdale, Arkansas, to Eureka Springs, Arkansas, along with their sister, Jinger, 20.
Jessa's scavenger hunt included a trip to a miniature golf course (she had to get a hole in one to get the next clue), collecting a dozen roses from strangers in a park, taking a trolley ride while answering a quiz, and riding a train with other members of her family – until she finally reached the destination: Thorncrown Chapel, a beautiful glass chapel where Seewald was waiting with a question, and a ring.
"I walked in and he was standing there at the front," Jessa says. "I could barely talk. I knew he was going to propose. I cried."
Planning for a WeddingAfter she said yes, Seewald slipped a .75-carat princess-cut diamond engagement ring on her finger. The two are now planning their wedding.
"I think my wedding might be similar to Jill's in a lot of ways," Jessa says. Jill and her husband, Derick, recently revealed they are expecting a baby. "I don't want to spend a whole bunch of money and buy a new set of decorations. We will save that money for the honeymoon."
The couple's family are celebrating the couple's engagement.
"Michael and I could not be more thrilled for Ben and Jessa," Seewald's mom, Guinn, tells PEOPLE. "Having similar goals and interests, they balance and complement one another beautifully. We praise God for the blessing of this relationship between Ben and Jessa."
The Duggars also are excited about the news.
"Ben asked me about asking Jessa to get engaged," Jim Bob tells PEOPLE. "We had already talked to Jessa about this and was 100 percent on board. I told him that Michelle and I were in agreement and supportive."
For much more on the couple's engagement – and details of her sister Jill's pregnancy – pick up this week's issue of PEOPLE, on newsstands now