The LP that Steven picks up in Sheba's workshop is "Kaleidoscope" by Siouxsie and the Banshees (1980). The band's song that plays over the scene, however, is "Dizzy," which was first released as a single in 1992.
Steven is stated as being fifteen years old and in Year 10. Pupils become fifteen during Year 10 (except in exceptional circumstances). Later in the film, Sheba states that he is going to be sixteen in May, i.e. he was already fifteen before entering Year 10.
When Sheba confronts Barbara about her diary, the makeup (eyeliner) she has smudged by crying changes. One moment she had dark thick eyeliner on, the next moment she has very little of eyeliner still on, and then the eyeliner comes back as before.