If this person still wants to see you, and they may, continue to do so. It may be that they are just not ready yet, or fear commitment. See where it goes. Some who turn down a marriage proposal will be of the mind that it is over. It does not have to be. After all, they say love is patient. Also, try to understand why the turn down, and have a heart to heart. This person may not be ready yet, and you may ruin a good thing by pushing for more
Just remember nothing is new under the sun someone was rejected before you and made it remember it is not the end of the world and as long as you have breath you have a chance for love, marriage the whole works the best to you.....
Maybe the person you proposed to wasn't ready to get married. Just be patient , maybe soon she will marry you.
Maybe the person is not ready of that yet. If he or she is still with you just wait a while and I'm sure they marry you.