GTA 5 car?

So I recently started playing GTA 5 and only played story mode. I'll still do that until I finish the story, I mean. But I have a small problem. I bought a car from Franklin with my money. First I had to buy a garage of course, and then I drove it to my garage at home and then took it to the airfield for a side mission. I just left the car there and then when I wanted to drive it again it was gone. It wasn't in the garage, or at the airfield, or at Franklin's house.

Can anyone help me and can I even get my car back?

Thanks in advance!