Seems like I am resident alien

The last sentence of second paragraph of page 44 shows "Social security and Medical Taxes are not withheld from pay for this work(OPT) UNLESS the student is considered a resident alien "

I've been to US for 3 years. On the basis of the criteria listed on page 5 of document, I am a resident alien. Tell me if am wrong.

Based on above mentioned, I need to pay Social Security and Medical Care because I am a resident alien. Am I right? Any hint is appreciated !!!

reference :
US TAXES for Aliens
http://www.irs.gov/pub/irs-pdf/p519.pdf

Many thanks,

Yuan