It is a big decision not only for you but for her also! Give her a little time to come around. I wouldn't take the ring back myself until I had a nice talk with her to find out whats going on! Make sure she is in the mood to talk though or it could end in disaster.
(Mark my husband wanted me to write you a female perspective...)
Put the ring on your desk in her plain view. Let her talk to you about it. But I wouldn't bring it up. If she sees you still have the ring then she will know where your heart is and you don't have to say a thing. If she ever wants it you can give it to her and if she doesn't let it go. Can't get married unless you are both very sure.