Those lyrics don't make sense to me, but hey, I'm old lol.
But, a jackpot is what you win when you gamble. So, if you were at a slot machine at a casino and you win the big prize and the bells start ringing and money is pouring out of the machine - you just won the jackpot.
So, it's also an idiom for when you win a prize or you get something great. You could say, "Wow, he really won the jackpot when she agreed to marry him."
When, they talk about gathering up the jackpot, they mean grabbing all of the money you won. Like all of the money that poured out of the slot machine, or taking all of the money you won off of the table if you were gambling with cards - you would gather up your winnings, or gather up the jackpot. Another term would be to "rake in" your winnings. Like in roulette, where the casino worker uses the little rake to grab the chips with.