Yes, you're sending 3 bytes (four atually if you count the command byte ($03)) but what Richard is saying is that $100 does not fit within a byte and according to the manual it will then get truncated to 8bits so in effect your shiftout statement send 3,0,0,0. Are you SURE you don't see a short pulse on the FC-pin? Try
Code:
DoIt:
  LOW RST
  SHIFTOUT TC, SCLK, 5, [$AA,$AA,$AA,$AA]
  HIGH RST
  Pause 2
Goto DoIt
Set the scope to trig on the falling edge of RST.