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.

Code:
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.
Code:
 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.