How a register shifts information to right at positive egde of clock
The sequence to be detected is (x1,x0)= 3,0,2,1. x1 is MSB, x0 is LSB. The output should therefore be triggered '1', when the four Flip-Flops are in the state:

x1 : 1 0 1 0
x0 : 1 0 0 1

But in your circuit, things are reversed. You have implemented it as x1 = LSB and x0 = MSB. Rest of the circuit looks fine.