@Ahmed Alfadhel,
One other thing to note is your scope was AC coupled in your pictures so you were "seeing" a bipolar waveform of -1.28v to +1.28v.
If you had DC coupled, the waveform on the scope would have shifted up and you would have observed the 0v to 2.5v the DA was outputting.
To get an actual bipolar output, you need the opamp level shifter/scaler.