The AMR26 is the Silverstone-based team's first car under the technical guidance of Adrian Newey, who joined from Red Bull last March.
The car has caught the attention of rivals but was late to hit the track in last month's Barcelona shakedown and has also lost time in Bahrain this week.
“We’re still learning the car, the engine, but we have a lot of work to do, and catching up to do. We have probably 400 less laps than the competition, (from) Barcelona and everything that we missed," said Stroll.
The son of team owner Lawrence, Stroll said Aston Martin had to get to grips with "a combination of things: engine, balance, grip.
"Right now, we look like we’re four seconds off the top teams, four-and-a-half seconds. Again, it's impossible to know what fuel loads and everything people are running. Now we need to try and find four seconds of performance, so we’ll see.”
Teammate Fernando Alonso agreed that Aston Martin needed to unlock more performance.
"We are a little bit on the back foot, we have to admit that, but hopefully there is time to improve," he said.
“On the chassis there is no doubt, we have the best with us. After 30-plus years of Adrian Newey dominating the sport, I think no one will doubt that we will find a way to have the best car eventually.
“On the power unit, we need to wait and see when we unlock all the performance, where we are and what is missing, and then work hard.”
Aston Martin, seventh overall last season, are starting a new exclusive partnership with Honda after previously using Mercedes engines.
The season starts in Australia on March 8th.