F-visa in Hong Kong (Guangzhou)

Hi!
I'm "working" on an F-visa. I'm on a program called TTC (Teach and travel China) which ends 15. January. I want to visit Macau and Hong Kong before I enter China again to start an internship in Shanghai for 6 months.

My questions are:
- Is F-visa the correct visa?
- How can I get double entry on the visa? I was only giving 1 entry when applying this summer.
- other things I should consider when applying in Hong Kong? (I want to do it express)

Best regards,
Lene