Visa's extention, anyone help?

Hello,
I got in mainland a new M type few months ago for continueing intership here in China. It expires in the middle of April. There is a remark which says - "Permitted to stay until 20 April for this time and to stay for 90 days each time since the next entry". So, does it means if I will go out of mainland before it expires and come back to mainland again, my visa automatically will be extended for extra 90 days and I will be able to stay in mainland till July? Am I right? Thanks!