outline should follow the fissures on the occlusal. isthmus width of 1.2mm..use the hatchet to check. as you extend towards the M and D, extend the prep B & L'ly. The buccal wall of your proximal box should be shaped like a reverse S (and break contact), the lingual wall should just break contact. The axial width of your box should be 1.5mm.
By the way, were you not taught the outline? I'm sure every professor teaches it a bit differently so maybe you should check with your prof, right?
Yeah, I know what you mean by not knowing the exact outline - we had to do max 1st molar class II's without being actually shown the outline. Your rule of thumb is always to just follow the grooves, and only open the contacts on the box as much as you need to - any more will take out needed supporting tooth structure, and less won't open the contacts.
Just take a sharp pencil and trace in where you think the walls need to go - if you look at the tooth from above the outline should start to be clear. Be careful though, you may need to drop the box not quite as deep on the distal because the curve of Spee. Man, I just love that phrase... good ol' curve of Spee.