AS long as you have your I20 signed by the DSO and your I20 is valid there should be no issue. However, since times are tough you never know. It is best to give yourself at least a year before your visa expiration if you are planning to visit. Or else let the visa be expired and still be in school and have your visa renewed  from Mexico (the easiest and hassle free way of doing). Let me tell you my experience:

I have my 4-years visa expired in march 07. I decided to go to Mexico to get my visa renewed in March 08 (the second last semester in my 4 years college). I did get 5 years M visa, I went to Nepal in Summer. Did n't have any problem at PoE. During my interview in Mexico, they asked me if I still went to the 4 years where I had applied for and told me pick up my pp @ 2. I have had a friend of mine did the same thing , he did have no problem. Again, it just fear inside you. You should be okay.