Xevos, you say that Maggie trusts you - but the truth is that she doesn't trust you. If she trusted you, she wouldn't believe you were still dating Ashley.
Rather than crawling or pleading or trying to persuade otherwise, I suggest you man up and stand up for yourself. If Maggie raises this issue again, tell her that if she thinks you're that type of person, then the two of you should not be together. Tell her that you deserve a partner who trusts you and will accept nothing less. If she continues with the distrust, dump her.
Yes, you may lose her - but you DO deserve a partner who trusts you. And getting into the mindset of walking away from someone who doesn't treat you right will set you up well for a future of dating.
Lastly, when this relationship eventually runs it's course - don't do long distance again. They only end in grief. Look for a girl who can be with you in real life and hold you - and kiss you - and hang out and do fun stuff with you.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.