stay in usa or go back to hong kong

Of course stay in US and get a degree! Your US degree will worth more when you try to look for a job in HK. Also, you will get more experience if you can practice at school or thru research.

If you really want to go back to HK and study there, you can go to their site and search for application. Most schools have application online now and it is easier to apply as a foreign student. (So you are applying as international student rather than local student. It might be a little bit more expensive the first year but it is easier to get in than local student.) Here are some of their sites:

HKU: http://www.hku.hk/prospectus/ug/app/app_01.html

CUHK: http://www.cuhk.edu.hk/adm/

HKUST: https://www.ab.ust.hk/arr/adm/

And you can search for other school online.

Stay in US to finish it &don't even think twice as this is definitely the better option!

I think you should stay in the US and go on with your studies. You will have an education background different than your peers if you ever decide to go back to work in HK. Not to mention you will have better English communication skills, some employers will value your exposure in the US and hence add points to your future career.

If you are going back to HK now, you will be competing with HK graduates and it's very hard to "stand out from the crowd"... so study hard now, and get good grades, and perhaps make use of internships in the US if you can find one (esp making use of the 12-month Optional Practical Training period) and get work experience in the US.... then later when you go back to HK, you will know your background and exposure will be extremely benefitial to your career.

I suggest you finish you nutrition degree in USA because not all HK universities will accept your asso degree. Also, not everybody have the chance of foreign exposure. So, i would suggest you finish your nutrition degree in USA and would better have pratical experience in that field.