(1) You don't need to "format" by writing zeros. Writing the image should be enough. (2) Without
count=No space left on device is expected. Your attempt with count= is explained by the above comment. (3) The commands you tried should have written zeros to the whole device. The fact there are non-zero bytes is disturbing. Each of your dd commands should have printed a summary (so many records in, so many records out etc.). What was the summary in each case?