I absolutely love FL studio. one can do such amazing things with it.
Just a few questions to help me understand your issue;
Have you added an audio clip as an instrument, then added the clip into that?
Then, are you playing the clip in the main playlist as the song, not the pattern?
Remember not to select any of the buttons on the actual pattern you have the audio clip linked to. Then it would start again every bar. If you have selected one, then deselect it, then add the clip into your song editor.
so if it looks like this;

Then that is your problem.
It would play through looking like this;
Note, I have selected "song" as my playback choice, not pattern.