There sure is confusion between .mp4 and .m4v because people think they are different when they are not. These 2 suffixes can be applied to MPEG-4 video files that are exactly the same in every way. Double-click the file and there'll be different behavior: .mp4 opens in QuickTime Player whereas .m4v opens in iTunes by default. But drag-and-drop onto either application will open either file type. I hope that helped you out.

thanks i got nervous because i didn't want to redo everything i've already done

the differences between the mp4 and m4v container extensions are subtle and nothing to really be concerned about since the actual video data encoded can be identical. It might be said though that an m4v extension is more correct though since an m4v would be used exclusively for video files. m4a should only be used for audio files. However, mp4 extension can be used for audio files, video files or video+audio files. Knowing all this, I would agree that m4v is a better choice.