Can I prevent my retainer from rubbing against my gum?

I have a retainer for the top of my mouth and it rubs against my gum making it very sore and VERY painful. My orthodontist recommended rinsing with warm salt water to help heal the gum, but it still hurts! I also don't want to take my retainer out for to long because I'm afraid my teeth may shift. Is there anything I can do to prevent the rubbing? Please help!!