I honestly just dont know how to beat the boss, help would be greatly appriciated

Dungeon 7 is that unpleasant horse one, right? My least favorite dungeon by far, in terms of mechanics, balance, and map design. Wish I could remember exactly how I did it (I reluctantly tried going through the dungeon and re-fighting the boss again just now, but I am too high level now for that to be indicative). But I think it was something like... Kyouko was the one being ridden for me so she couldn't do anything helpful, Mami debuffs with Disorienting Shot and Distracting Shot, Madoka uses Glitterdust on Sayaka then if possible uses String Shot followed by just attacking normally, Sayaka opens up with Parry Stance and then unloads with her most powerful physical attack (which here became the kick attack that is exclusive to this dungeon). Sayaka was the source of basically all the damage, after debuffing the boss everyone else was just there to direct hits away from Sayaka (via Glitterdust). Even with all this, it was still really close, with Sayaka being the only one alive at the end.

If Sayaka is being ridden for you, Kyouko would probably be an acceptable substitute, since her entire thing in this is being the party's versatile jack-of-all-trades-master-of-none. If Mami or Madoka are being ridden, then I dunno. This boss is indeed OP.