Hi and Welcome!
Such happens. Please read the manual of your car stereo in order to see what kind of media is supported at all. Support for MP3, WMA or other formats besides CD audio is not common.
I know I should have made an audio CD but it would only fit about 80 minutes of songs. What should I do so I can play more songs from a single CD?
If your car stereo does only support audio-CD, then your only options are either to replace your car stereo or attach a CD changer (this must be compatible to your car stereo unit). Another idea: if your car stereo has a line input, then you could attach a MP3 player.