I want to repeat the last ~6 seconds of my track in a blending fashing to extend the song for a few minutes. All I know how to do is cut the end, and repaste it, but this leads to a bumpy transition. This is my first time trying to do something like this, so can anyone with experiance tell me how I can do this?
This is always easier if you're using a DAW with tempo that you've worked to right the way through the recording. Doing it 'freehand' is harder, but still possible, with care.
This may depend on whether the song actually ends or is going to run to fade, but the simplest trick is to keep moving back a beat until you find a cut point that works at both ends.
Note that you must cut like to like. It's no good trying to cut from a large to small arrangement unless you have the full multi-tracks. Back in the tape days we used to spin in reverb tails on a spare stereo pair, if we had to cut to a drop section. Making a 12-minute 12" dancefloor mix out of a 3 minute single was very popular back then ;)
e.g if you're going to loop 4 bars & your song has an actual ending after the last repeat, then you cut at beat 4 before the end & the same 4 bars earlier. Always cut at a zero crossing & never right on a beat; always cut slightly before - this is a lesson learned from when these cuts were done on physical tape. It still can apply now, even if you have modern crossfades to help you.
If you're doing this by eye, then just before a kick drum is always easiest to spot.
Test your loop. If it doesn't work, reassemble it & cut instead at beat 3… you may find you end up cutting on 2¾ if nothing else works to avoid an obvious cut-point. Trial & error is so much easier now you have an Undo function ;)
Once you get your smoothest potential cut points, you can then smooth it further with a short crossfade. Get the cut right first before leaning on the crossfade to hide your mistakes.