All looks good, except:
3. You have combined two idioms!
10. "at the back of the car" - a different preposition would be more idiomatic.
12. "At the back of my mind" tends to appear at the beginning of the clause or sentence; it then tends to be followed by a quite long explanation.
15. The context here is difficult to imagine.
19. Cf. some of your other examples...
All the best,
- For Teachers