Declining Invite After YES Reply

An old friend of mine from college that I just recently reacquainted with invited me to his wedding which is less than a week from now. I said yes, with guest, however, now I am over booked with work, international travel and family commitments. I would of course send a gift regardless, however, is it to late to politely decline? What is the best method of declining or should I just suck it up against all my wishes. Thank you!!