entering the u.s. for the second time in one year

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I graduated and legally worked wiht my opt in the u.s. until september 2005. I then left the U.S. for four and a half months to Peru where I was working a volunteer job. 1/24/2005 I re-entered the U.S. on my 10 year multiple entry visa to visit some colleges and get some tours for ym Masters and was granted 2 months on my I-94. I left the day prior to my I-94 stamp which was March 29th and returned to Peru (I am a salvadorean citizen but my parents live here and I work here at a volunteer position with a non-profit). My fraternity brothers are graduating May 20th and I would like to go back for their graduations and to travel around the U.S. for a bit with them since they are all international students and returning to their home countries and I also want to meet with some more colleges. But I am very worried that I may be denied entry at POE due to the fact that I spent 2 months in the country 7 weeks ago. Is that a possibility or is there more chance that I will not have a problem? I have had a visa to the u.s. since i was 5 and have never stayed past my date nor been illegal at anypoint. Is there any paperwork I need to demonstrate to officials so I don't have any problems? I intend to return to Peru in July or August to continue my volunteer position until I apply and get accepted to a Masters Program in the U.S. Please, any help will be most beneficial and I thank any responses in advance. In case this is necessary, I am a Salvadorean, 25 year old male, I dont know how relevant that information may be. Please help. Thank you