You don't need to go back to China for the F1 visa. It is statutorily allowed to change nonimmigrant status in the US. As long as you file the petition with the USCIS prior to the expiration of B2 status, you can lawfully stay in the US while waiting for the result. Once your petitin is denied, you will have to leave US as soon as possible, so that the unlawful stay will not accrue. (there is a three year bar and a 10 year bar.)

Of course the status change application of this kind is difficult to get approved. No attorney could guarantee it. Among other things, the focus of the application should be on the explanation to the USCIS why you are applying for the status change, that you did not intend to change status in the US when you applied for B2 visa in China, and that your application is not intended to extend the stay in the US.

Good luck.