You're pretty much doing a high bar squat where the bar is lower than usual. In addition to the things you've noted, stop at the top of each rep. Don't look up. I thik your stance is too wide, but can't tell for sure in this video. There are two platform videos on here you need to watch that deal with back angle (featuring Rip and Chase) and one on looking down (featuring Tom Campitelli and a lady).