Reduce the stamp size created using javascript

have javaScript to create stamp its working fine, but stamp size is little big, i need to reduce size of stamp, please help me

have use below code in custom calculation script

var cAsk = "Enter stamp you want to give";
var cTitle = "Document state for stamp";

if( event.source.forReal &&
   (event.source.stampName == "#stamp1"))
{
  event.value = app.response(cAsk,cTitle);
}