Great.
Ok, I hope I can explain this next step well enough ...
Press U to get the Shape Tool, then click and hold on it to get the Line Tool. In the Options Bar you'll see where you can choose "Weight". Enter 6px there.
Also in the Options bar (I can't give you a screenshot, because my version is different) you need to choose the option that says "Subtract from shape area". On mine I can hit the shortcut key - (dash/minus), maybe yours will do that too.
At this point I suggest lowering the opacity of your green line layer so it's visible but fairly faint.
Then return to your shape layer. Make sure you have the mask selected (a border around it in the layers panel).
Then draw a line with your line tool following one of your green lines. Make sure you start and finish it OUTSIDE the truck shape.
If it works properly, it will subtract that line from your black truck shape.
If so, great! Repeat for the other lines.