Issue with Audio Overlay in Adobe Spark

hi there,

I am new to Adobe Spark and really wanted to input my own audio recording over the entire video without having it stay with one specific slide, so I pre-recorded it and uploaded to music section and then it played throughout the video. However, I have to make sure it is the exact right length to my video or it starts over. Is there a way to do that better?

Also, I wanted to be able to play a background music while I also played the voiceover. It seems you can only do one or the other?

Thanks!