No woman in her right minds would gladly accept your proposal for sex in the very 1st encounter unless she is a hooker. Since you said you fancy her a lot, try to ask her out on a date, and if she is interested in you, she might accept your request and might come out with you; from this, try to gradually build up a rapport with her and drop small hints about your interest in her and if she is smart enough she would tell you her answer.
There is no rule book that says you should approach a woman in a particular way; you can go meet her and start a conversation with her; if she responds back with interest, you can deduce that she is interested in you, however if she doesn’t accept her decision and get over your fantasy.
Even though you haven’t asked I would like to add a line about your habit of masturbation; limit it to 2 times a week because chronic masturbation has its downfalls. Good luck.