You have to pay it, otherwise IRS will look for you.  If you are working for somebody else, your employee will deduct from your pay check (If my memory serves me right 6.2% of your paycheck, and employee will pay the same amount for you too. ifyou are self employeed, you will have to double the amount. 

correct

那如果我今年想用RESIDENT报税 （还是F1），可是我的W2上没有扣除这些税（估计还是按照NR算的），我需要补交吗？