xml schema Validation script prevent nesting

I am trying to create an xsd file run against our web.config files. I am trying to catch human error and prevent nesting of tags. Example of bad xml:

<applicationSettings>
   <app.MySettings>
       <setting name="FirstName" serializeAs="String">
         <value>John</value>
            <setting name="LastName" serializeAs="String">
               <value>Smith</value>
            </setting>
       </setting>
   </app.MySettings>
<applicationSettings>

You will notice the Setting "LastName" is nested inside of "FirstName". The correct format is:

<applicationSettings>
   <app.MySettings>
      <setting name="FirstName" serializeAs="String">
         <value>John</value>
      </setting>
      <setting name="LastName" serializeAs="String">
         <value>Smith</value>
      </setting>
   </app.MySettings>
<applicationSettings>

So, I'm trying to create a schema to run it against. I have this so far:

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://ift.tt/tphNwY">
    <xs:element name="applicationSettings">
        <xs:complexType>
            <xs:choice minOccurs="0" maxOccurs="1">
                <xs:sequence>
                    <xs:element name="app.mysettings">
                        <xs:complexType>
                            <xs:choice minOccurs="0" maxOccurs="1">
                                <xs:sequence>
                                    <xs:element name="setting">
                                        <xs:complexType>
                                            <xs:choice minOccurs="0" maxOccurs="1">
                                                <xs:sequence>
                                                    <xs:element type="xs:short" name="value"/>
                                                </xs:sequence>
                                                <xs:attribute type="xs:string" name="name"/>
                                                <xs:attribute type="xs:string" name="serializeAs"/>
                                            </xs:choice>
                                        </xs:complexType>
                                    </xs:element>
                                </xs:sequence>
                            </xs:choice>
                        </xs:complexType>
                    </xs:element>
                </xs:sequence>
            </xs:choice>
        </xs:complexType>
    </xs:element>
</xs:schema>

Something is wrong because I get back its valid which it shouldn't be? If this is the wrong way to do this (using schema) please let me know of a better way.

Thanks!

D H