It's unlikely an unfinished pipeline for export purposes had a significant impact on current gasoline prices.
https://apnews.com/article/fact-checking-895299166310
"Experts tell The Associated Press that the Keystone XL pipeline cancellation isn’t affecting what’s happening in the oil market today. It was never operational when it was shut down, and was not slated to go into service until 2023, according to a press release from TC Energy, the company constructing the project."
"Even if the Keystone XL pipeline had been completed, the amount of oil it was designed to transport would have been a drop in the bucket for U.S. demand, experts noted. The U.S. used nearly 20 million barrels of oil a day last year, while global consumption of oil was near 100 million barrels. The pipeline would have contributed less than 1% to the world supply of oil, according to AP reporting."