so basically you don't have to take the target lock to get the boost, but you must be in arc at range 1-2 to boost
The may doesn't work like that. It's used fairly often on action cards, but you always have to do the whole action, you can't break the action into different parts and only do part of it.
For example Marksmanship says "you may change one of your [eye] into a [crit] and all other [eye] into [hit]. You can't do only one part of that, you have to do the whole thing.
Same for this Droid, it's all part of one action so you have to do the whole thing. The may part simply means you have the option of doing this, it's creating an option for the first part of the action.
R2-D2 uses may, Advanced Sensors uses may, Push the Limit uses may. However Gunner does not, meaning the 2nd attack isn't an option.