<form method="post" action="//submit.form" onSubmit="return validateForm();">
<div style="width: 100px;">
</div>
<div>
<div style="float:left"><a href="" id="lnk100" title="form to email"></a></div>
<script src="https://www.100forms.com/js/FORMKEY:EBTR2NWCLUZ6" type="text"></script>
</div>
<div style="display: inline-block; text-align: center; padding-bottom: 18px;width : 450px;">
<div style=" margin-left : 15; margin-right : 1%; width : 49%;">First name:<br/>
<input type="text" id="data_2" name="data_2" style="width: 100%;" class="form-control"/>
</div>
<div style=" margin-left : 15%; margin-right : 0; width : 49%;">Last name:<br/>
<input type="text" id="data_3" name="data_3" style="width: 100%;" class="form-control"/>
</div>
</div><div style="padding-bottom: 18px;">E-mail:<br/>
<input type="text" id="data_4" name="data_4" style="width : 450px;" class="form-control"/>
</div>
<div style="padding-bottom: 18px;">Contacto:<br/>
<input type="number" id="data_1" name="data_1" style="width : 450px;" class="form-control"/>
</div>
<div style="padding-bottom: 18px;"><input name="skip_Submit" value="Confirmar" type="submit"/></div>
</form>

<script type="text/javascript">
function validateForm() {
if (!validateEmail(document.getElementById('data_4').value.trim())) {
alert('Email must be a valid email address!');
return false;
}
return true;
}
function isEmpty(str) { return (str.length === 0 || !str.trim()); }
function validateEmail(email) {
var re = /^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,15}(?:\.[a-z]{2})?)$/i;
return isEmpty(email) || re.test(email);
}
</script>