I didn't look at everything in the script, but with your problem maybe this will work.
This should go before the var %shoot = $int($2) line.
if ($2 > $readini(Points.ini,$+(#,.,$nick),Points)) {
msg $chan $nick you cannot bet more points than you have.
}
I also recommend making it where they can't gamble negative points as well, to rapidly inflate their point totals.
Something like this would work.
if ($int($2) == $2 && $2 > 0) {
This will ensure that even if they lose that it won't add points instead.
Hope that what I have here helped.