Yeah the others are right. I think she is using that ring to hold on to you. She wants you around in case things don't work out with her current bf. She also wants you around in case all of her other plans don't work out. Why would you want to be her second choice, if that. If she wanted to marry you, she would have made a decision by now.
I think you already know the answer to how she is feeling about marriage with you. You just need to finish things up by getting that ring back.
The only way you will take the pressure off is by getting the ring back and letting her know the offer stands if she would ever change her mind in the future. (Personally I wouldn't offer again, but just trying to make this easier for you.)