Leave her (For some time).
What guys don’t know about girls psychology is that girls love to ruminate in their thoughts. They will think about what you said, again think and then again think…and each time they will reach at different conclusions. Give her time to think about you.
Girls are like that only. When they say they need time, they really need time!
Never propose a girl twice and that too in succession. Take at least a gap of one month.
Now what ? Give her a break of one week. Then restart your efforts. But this time just miss the proposal part completely. Start fresh as if you have seen her for the first time.She will be amazed, bewildered,confused, relieved all at one go by your behavior. If you can’t make her your girlfriend, make her your friend!
Girls hate absolutely to be friend zoned by their lovers (Read fans). Either she will love you or leave you but cannot linger you.
Caution : My advice is not suitable for over cautious intellectual girls, who see through your every move. The best way to win through an intelligent person is by being honest. Never play games with an intelligent person.
PS : This also implies that my advice doesn’t suit me!