Matt,
I am trying to figure out why AF lock doesn't appear in the viewfinder. It should blink (*) but it doesn't.
The reason why when you press the (*) button that the AF doesn't lock focus is because the (*) button is an AE ( EXPOSURE) lock , when you press that all your doing is locking the metered exposure .
The button next to it ( to the right ) is for selecting which AF point you are going to use .
To have the camera so that you can lock focus and then recompose , do this ;
On the lest side of the top plate , press the "AF" button while rotating the front dail until "ONE SHOT" appears on the LCD screen .
Not "AI SERVO" .
You will have single shot AF rather than continuose .
Next while pressing the "AF" selection button , turn the dail until the AF point in the viewfinder that you want to use is selected .
Finally .
Turn the "EYE CONTROL" dial to "OFF" .
When you try to learn how to use the seperate functions , try to calibrate this function then , or just leave it switched off .
By doing the above you can now lock focus and while holding the shutter release button in the same position , recompose then fully press the button for the shot .
Regarding exposure ;
Set the ISO to what you want , as you have done .
Don't enter any exposure compensation unless you need to .
Don't press the "AE-Lock" button unless you need to .
If the scanned negative come back duller than expected , it's because the firm that developed and scanned your film did not know you wanted them overexposed , because you didn't tell them you did .
And because for some mad reason you haven't got your negative back , just a scan , there's not a lot you can do about it .
Always keep your negatives .
If in doubt , read the manual ;
http://www.cameramanuals.org/canon_pdf/canon_eos_3.pdf