I feel like a big whore :,(?

[...?]

Definition of the word whore: n.
1. A prostitute.
2. A person considered sexually promiscuous.
3. A person considered as having compromised principles for personal gain.

You are not any of the definitions above. You're a human being who made a mistake, just like everyone else has done - myself included. Telling your mom what you did was very good of you.

So, how do you gain her trust back? Well, first you have to understand how important trust is in a relationship. It will take time for her to trust you again - how long it will take I can't say because I don't know anything about your mom or what she's like.

To begin, if you haven't done so already, admit what you did to her was wrong and apologize. Don't make any excuses - accept responsibility for your actions or else admitting what you did was wrong and apologizing to her will mean nothing (if you've done all of this already then forget this part). You can also show her you're trustworthy by not ever doing this again. Don't do things behind her back and make sure to be honest with her about things. You might even want to consider letting her have access to the private areas in your life for a while - meaning, giving her access to your Facebook account, email, Twitter, diary, or whatever you have that's private or consider to be private, so that she can see you're not hiding anything from her.

Good luck with everything.