Right now you got 10% chanse to win 3x gold, 35% chanse to win 2x gold and 55% risk of losing.
You can increase the first interval to make it less likely to win.
For example:
local t = {
[{1, 70}] = 0,
[{71, 90}] = 2,
[{91, 100}] = 3
}
This gives 10% chanse to win 3x gold, 20%...