Wirelessly posted (Opera/9.60 (J2ME/MIDP; Opera Mini/4.2.13337/786; U; en) Presto/2.2.0)
This wasn't clear to me from the OP's post.
Was the "extra" pillow in the F section overhead bin? Or was it in the Y section overhead bin?
If the pillow is in the Y bin, the FA should have let the OP take is since it is clearly an "extra" pillow.
If the pillow is in the F bin, then the FA acted correctly and the OP shouldn't have taken the pillow.