Not necessarily... although probably.
Here's a scenario: The car had to get to the carpark and the policeman asked you how you got there, and you panicked and admitted driving on a public highway...?
In that case, you could be looking at your mum being done for loaning a car to an uninsured driver, and losing her car, or you being done for taking without permission, no insurance etc.
Just a scenario, but probably never come to that. But it might make you think in future. By the way, it sounds like you're being mature about this, but can I ask how you'd manage if someone had been hit by you - say a kid? How would their lives have been affected with no insurance back-up? However, I'm sure you've thought about all that since, and your current attitude is commendable.