They need to roll 80 or higher to win by default. The 98 is the 3x part, which is what you want to change. So you would want this, unless you want them to have to roll exactly 80 or 98.
@if@[>=||@rand@[1|100]||80||@if@[=||@rand@[1|100]||98||Rolled @rand@[1|100]. @user@ won @calc@[*|3|@target@]
^With this, if they roll 80 or higher, they win 2x, but if the number is exactly 98, then win 3x.