Question about MRI signal construction
I would expect that you simply cut the outer parts of the image away. Certainly, there is always a hassle to figure out the proper pixel in the center, but that is a detail of the FT-algorithm employed.

Remeber: Sampling denser than you need increases the FOV. Hence, the image you simulate should simply be larger with the original image (that you get by simulating 128 sampling points in the setting you described above) sitting at its center. Cutting off the outer void parts is therefore the technique you need, and not an interpolation technique.