How do I regain my mothers trust??
Your mother's trust in you will return in time. You've already taken a big step by telling her the truth. All she needs is time to accept and deal with what you told her and things will become clearer to her soon enough.
Just keep being honest with her - no matter how tough it seems.
it mostly just takes time. but in that time, try not to do anything that will break her trust more because it will take longer to get it back