An e3 exam is where you answer questions, and if you don't get 70% you can pass it by going through it with your tutor, so don't worry about it. The e4s are harder, as you have to get almost every one right to pass
I don't know what unit you are on, but from what you've done, I imagine it will be your shampoo unit or styling unit, so revise on things like the hydrogen bonds in the hair structure and how it's affected, as well as the shampooing techniques, and what each type of shampoo/conditioner does e.g. Lemon will dry out oily hair, coconut will moisture dry hair etc.
You can usually find the questions you'll be asked in your portfolio on each unit
good luck xxxx