just barely (do something)

When you succeed in doing something but come really close to failing, you can say that you "just barely" did it. In the example above, you did return the car on time but you almost didn't do it on time. Another example:

I took French in high school, but I just barely passed it.

make it back (to somewhere)

To "make it back" to somewhere means to successfully return to your home or to the place that you left from:

Hasn't Doug made it back yet?

(do something) in time to (do something else)

You use the phrase "___ in time to ___" when you're talking about an action that you have finish before a certain time in order to do something else. For example:

I managed to make it back home in time to watch the last episode of Lost.

In this example, the action you have to finish is "make it back home". You had to do this by a certain time in order to watch the last episode of the TV show Lost.

return (something)

When you borrow or rent something, the phrase "return ___" means to give it back to the person who owns it.