Wire the pig tail back on if you would like to use the connector to daisy chain more lights. You could just leave the chopped end and cover it with electrical tape if you want.
For wiring a pig tail (connector):
Best to use a multimeter and figure out which wires correspond to which pin. This is a guide but I suggest checking for yourself to be sure; https://www.wiredwatts.com/learn-connectors
Then look inside the last pixel, the wires going out should have text above it.
+12 or +5 is power, DO is data out and GND is negative.
Sounds like you have no intention of daisy-chaining another string or more pixels so in such a situation I cut the wires to slightly different lengths, fold them over, and heat shrink them putting the wire fold(s) inside the heat shrink. The wire fold creates a 'bump' in the shrink keeping it from working off or further on the wires. The different cut wire lengths help keep them from shorting if the insulation works back a bit or if moisture seeps inside the shrink.