Well you can start by typing out full words.
Firstly, is she in a relationship with anyone? If so then she's off limits - and no, don't try and change her
Secondly, if you think she's going to rejected you then you're already pretty much rejected yourself - how about some self-confidence, get to know her better so she's more inclined to say 'yes'
And thirdly, you're talking about marriage? That's some serious commitment - how well do you know her already? Have you gone out with her at all?
You post, you ask questions, you give facts --> I reply, I give quotations, I have opinions