A 3.5 inch (1.44MB) floppy can accommodate 1474560 bytes of data. The boot image is exactly 1474560 bytes in size.
Common mistakes when preparing the boot floppy are:
Not downloading the floppy image in binary mode when using FTP.
Some FTP clients default their transfer mode to ascii and attempt to change any end-of-line characters received to match the conventions used by the client's system. This will almost invariably corrupt the boot image. Check the size of the downloaded boot image: if it is not exactly that on the server, then the download process is suspect.
To workaround: type binary at the FTP command prompt after getting connected to the server and before starting the download of the image.
Using the DOS copy command (or equivalent GUI tool) to transfer the boot image to floppy.
Programs like copy will not work as the boot image has been created to be booted into directly. The image has the complete content of the floppy, track for track, and is not meant to be placed on the floppy as a regular file. You have to transfer it to the floppy ``raw'', using the low-level tools (e.g. fdimage or rawrite) described in the installation guide to FreeBSD.