Switzerland's Tanja Frieden claimed the inaugural women's snowboard cross gold medal in a dramatic final.
Gillings has battled back from a bad foot injury this season
American Lindsey Jacobellis had a big lead but crashed at the penultimate jump after grabbing her board.
Jacobellis appeared to be trying to impress the crowd, and fell before recovering for silver, while Canada's Dominique Maltais took bronze.
Britain's Zoe Gillings settled for 15th place after crashing out in her quarter-final.
The 20-year-old fell in the second elimination heat and came third in her last race to decide the minor places.
"I'm frustrated, but that's snowboard cross for you," Gillings told BBC Sport.
"I was really nervous at the top and then people got in my way and I was taken out twice.
"The luck wasn't with me in the quarter-finals, but to be honest I was probably lucky to qualify after my first run."
Jacobellis, who had enjoyed a big lead for almost the whole race, blew her title hopes with the finishing line in sight.
She tried a "backside method grab" on her board while airborne, but the move put her off balance and she fell.
"I was really excited - everything seemed to be going so well," she said.
"Then I landed badly. I got a bit frustrated because I have worked so much.
"The wind has just been catching me weird and I tried to grab and all sorts of grabs to see which one would work, to try to stabilise myself in the air. But it didn't work."
Frieden said she thought the chance of a gold had passed her by.
"It was just amazing," Frieden said.
"You are never sure until you get to the very end. This is something I have learned in races."
Pre-race favourite Maelle Ricker hurtled out of the fencing at the side of the course in the final and had to receive medical treatment.
Gillings had battled her way into the last 16 contenders after coming 12th in the two-run individual qualifying.
She was hindered by fresh snow on her first qualifying run but after her protest was rejected she responded with a second leg of one minute 31.03 seconds to qualify.
Gillings had gone to her first Olympics with high hopes of a decent finish after she ended last season ranked as the world number four.
However, the Isle of Man athlete is only just returning to form after she spent six months on the sidelines with a foot injury.
And Gillings said Jacobellis had no-one but herself to blame for missing out on a gold medal.
"I feel pretty sorry for her but it looked like she was trying to show off," said Gillings.
"I wouldn't have done it in her position."