I gt COS apprvd frm H4 toF1 bt no visa stamping.Cn I go on cruise 2Mexico?

My COS was approved in aug from H4 to F1 and I am currently enrolled in a reputed university.I will graduate in Spring 2013. But there is no visa stamping on my passport. I want to go on cruise to mexico in december for 3-5 days. Please advise if I can return to US without any issues.