Your data is anisoptropic. You can check the "Reorient images when loading" checkbox in preferences to interpolate the images, though note there will no longer we a one-to-one correspondence between screen pixels and image voxels. For future sequences, you may want to consider using isotropic sequences. 

You may also want to try MRIcroGL - I am glad that MRIcron has proved robust and popular, but I no longer have time to actively develop MRIcron.