Angularjs checkbox directive showing unchecked when rendering

I have a problem with this directive from http://ift.tt/2srlvgc.

The problem is that when the checkbox is initially rendering, the checkbox is unchecked. But, I have the "item.waschecked" equal "true" in ngModel.

I think the problem is "isChecked=false" in:

scope.checkboxModel = {
                isChecked: false,
                // checkedIconName: scope.checkedIconName || 'check_circle',
                // uncheckedIconName: scope.uncheckedIconName || 'radio_button_unchecked',
                // IE 6-9
                checkedIconName: scope.checkedIconName || '',
                uncheckedIconName: scope.uncheckedIconName || '',
                checkedIconColor: scope.checkedIconColor || '#009688',
                uncheckedIconColor: scope.uncheckedIconColor || '#B2DFDB',
                size: scope.size || 'small',
                showLabel: true
            };

What is wrong here?

Another question, in this directive, is possible show the label before the checkbox, setting an attribute?

//markup

   div sb-checkbox checked-icon-name="check_box" 
      unchecked-icon-name="check_box_outline_blank" size="small" 
     label="Mostrar na tela"  ng-model="item.waschecked">
  </div>

//directive

/* @preserve
 *
 * angular-material-checkbox
 * http://ift.tt/2srlvgc
 *
 * Version: 0.0.1 - 08/22/2015
 * License: MIT
 * Credits: sattvabitinc & contributors
 */
angular.module('sb.checkbox', [])
.constant('iconSizeClasses', {
    small: '24px',
    medium: '40px',
    large: '53px'
})
.constant('labelSizeClasses', {
    small: '16px',
    medium: '20px',
    large: '24px'
})

.filter('trust', function($sce) {
    return function(val) {
        return $sce.trustAsHtml(val);
    };
})
.directive('sbCheckbox', ['iconSizeClasses', 'labelSizeClasses', function(iconSizeClasses, labelSizeClasses) {
    return {
        scope: {
            label:'@',
            checkedIconName:'@',
            uncheckedIconName:'@',
            checkedIconColor:'@',
            uncheckedIconColor:'@',
            size:'@',
            preSelected:'@',
            showLabel:'@'
        },
        require: 'ngModel',
        restrict: 'AE',
        template: '<div class="sb-checkbox" style=\'-moz-user-select: none; -webkit-user-select: none; -ms-user-select:none; user-select:none;\' unselectable=\'on\' onselectstart=\'return false;\' onmousedown=\'return false;\'><span class="custom-icon" ng-style="{color: checkboxModel.isChecked ? checkboxModel.checkedIconColor : checkboxModel.uncheckedIconColor}"><i class="material-icons" ng-style="{verticalAlign: \'middle\', fontSize: checkboxModel.iconFontSize}"  ng-bind-html="checkboxModel.isChecked ? checkboxModel.checkedIconName : checkboxModel.uncheckedIconName | trust"></i></span> <span ng-if="checkboxModel.showLabel" ng-class="{\'sb-checkbox-label-checked\':checkboxModel.isChecked, \'sb-checkbox-label-unchecked\':!checkboxModel.isChecked}"></span></div>',
        link: function(scope, element, Attrs, ngModel) {
            element.css("cursor", "pointer");
            scope.checkboxModel = {
                isChecked: false,
                // checkedIconName: scope.checkedIconName || 'check_circle',
                // uncheckedIconName: scope.uncheckedIconName || 'radio_button_unchecked',
                // IE 6-9
                checkedIconName: scope.checkedIconName || '&#xE86C;',
                uncheckedIconName: scope.uncheckedIconName || '&#xE836;',
                checkedIconColor: scope.checkedIconColor || '#009688',
                uncheckedIconColor: scope.uncheckedIconColor || '#B2DFDB',
                size: scope.size || 'small',
                showLabel: true
            };
            console.log(iconSizeClasses['small']);
            var iconSizeClass = scope.checkboxModel.size.toLowerCase();
            if(iconSizeClass == 'small' || iconSizeClass == 'medium' || iconSizeClass == 'large') {
                scope.checkboxModel.iconFontSize = iconSizeClasses[scope.checkboxModel.size.toLowerCase()];
            }
            if(scope.showLabel == 'false') {
                scope.checkboxModel.showLabel = false;
            }
            if(scope.preSelected == 'true') {
                scope.checkboxModel.isChecked = true;
            }

            ngModel.$setViewValue(scope.checkboxModel.isChecked);

            element.bind('click', function() {
                scope.checkboxModel.isChecked = !scope.checkboxModel.isChecked;
                ngModel.$setViewValue(scope.checkboxModel.isChecked);
                scope.$apply();
            });
        }
    };
}]);