I like the composition very much. It's difficult to get things right in a larger view but macro is very tough with auto exposure. Nothing seems to be sharp in the photo-probably because of hand holding (setting up a tripod would have lost the opportunity) and it is overexposed :(
If your Pentax has full manual, that is where you ( and I ) need to concentrate now. Getting the exposure correct is essential--no matter what else is right, if the exposure is off even a little, the shot is ruined. I wouldn't worry about the spider's legs! Just being there long enough for a shot is something!