The offence of failing to stop applies "on a road or other public place".
Is a car park with barriers a public place? Probably not, but ultimately that would be for a court to decide.
It can get a bit complicated as it all depends on whether any damage was caused to the barrier that hit your car.
The law states
"If owing to the presence of a motor vehicle on a road, injury or damage is caused to a third party"
A car park is not deemed as a road, and if no damage was caused to the barrier then no crash has occurred therefore no offence committed.
But in the same vein, car park owners also have a statutory duty of care. The law states -
"Car park owners and operators are responsible for maintaining the safety of their premises, including barriers. This includes ensuring that barriers are maintained according to the manufacturer's instructions. Unsecured barriers can swing open due to wind, gravity, or vandalism"
There are also regulations and laws regarding installation and testing.
So on the face of it based on what you have said, no offence is committed, however, I would suggest you pop along to your local Police station with your documents, tell them what has happened and see what they say, because whilst not a RTC under the road traffic act, if there is damage to the barrier it may be treated as a criminal damage (different offence).
The Police may not be interested which will be no surprise to many) and if that is the case, take a note of the person you speak to whether they be a regular Police officer or civilian.
If there is damage to your car, you may well have a claim against the car park owners if they have breached their statutory requirements
Like I say, not as straightforward as it might first seem, but cover your backside anyway.