My dog doesnt trust me?

So today when i was training my dog. shes 2 and a half years old. A little old to be teaching tricks, i know. Anyway, i wanted her to roll over. and i showed her how and helped her like 50 tiimes. i gave her treats every time i made her do it to. But she still wouldnt roll over. So i yelled really loud at her because i was really frustrated, but now i feel really bad. My poor doggy, anyways, now shes scared of me. Shes really sensitive to sound, and she never really sees me mad. So, how do i earn her trust back? Its like shes seen a whole nother side of me and its like shes scared of me, and i feel soo bad. please help mee.... what should i do?