Merging two songs

I just recorded a mix using serato dj and because my mix was so long it split it into 2 different mixes. I watched a tutorial video to try to merge them to make it all one mix but it combined them together with one over the other when I played it, is there a way to merge the end of one song with the beginning of another?

Assuming that you’re using the current 2.0.5 version of Audacity;
Import both files (they will appear one above the other).
Ensure that they are both selected (Ctrl+A to “select All”).
“Tracks menu > Align Tracks > Align End to End”

Check that they play as you want.
You can adjust the position of the tracks using the Time Shift tool if you want them to overlap a little.

Export as a new audio file (File menu).

If you do this you may want to cross-fade the overlap by fading out one track and fading in the other.