If you want to end your song with a bang, make it a tremolo instead! What's a tremolo? It's a wavery effect that you make by stroking your strings very quickly, in kind of a peculiar way. Here's how:
Start with a thumbs-up: Make a loosely clenched fist with your strumming hand, with your thumb sticking straight up.
Place the pad of your thumb on top of the heel of the ukulele. The heel is the little flare of wood where the neck meets the body. The pinky-end of your clenched fist should stick straight out, perpendicular to the uke, as if you're shining a light out the end of your fist.
Point your index finger somewhere between the floor and the tuning pegs, whatever is comfortable, and NOT touching the strings.
Flick your middle finger out so it brushes the strings, like a soft strum, and just like a strum, brush the strings all as one unit
Flick that middle finger back up into your fist.
Repeat, slowly at first, slightly re-angling your hand to get juuuuuuust the right angle for the sound you want.
Increase the speed!
And now for the pièce de résistance: The fly flick. After you have done your tremolo for however long you want, take your thumb off the heel of the ukulele and flick the strings with your index or middle finger, as if you are flicking a fly off the strings.
Once you have done the fly-flick, your hand goes up in the air as if you have done the most amazing thing ever seen!
Things to keep in mind:
Your arm and hand should be pretty still. The only movement should be in your tremolo-ing finger.
You are brushing the thumb-side of your middle finger
This can take a little while to work up to the speed you have in mind. Just like anything else, practice makes pretty darn good!