How to Add Cross-Column 3 Gadgets Side by Side on Blogger

Go to Template tab in Blogger Dashboard and click the Edit HTML button. Now click once inside the Editor and then Press CTRL+F , A search box will appear in the right upper corner of the editor itself. Now search for "region-inner tabs-inner" (without the quotes) and you will see code like (this code would different in your template because of presence of widgets in crosscol section but the structure would be same )

<div class='region-inner tabs-inner'>
      <b:section class='tabs' id='crosscol' maxwidgets='1' name='Cross-Column' showaddelement='yes' />
      <b:section class='tabs' id='crosscol-overflow' name='Cross-Column 2' showaddelement='no'/>
</div>

Add the following highlighted code to it

<div class='region-inner tabs-inner'>
      <b:section class='tabs' id='crosscol' maxwidgets='1' name='Cross-Column' showaddelement='yes' />
      <b:section class='tabs' id='crosscol-overflow' name='Cross-Column 2' showaddelement='no'/>
      <macro:include id='crosscol' name='sections'>
            <macro:param default='0' name='num' value='3'/>
            <macro:param default='crosscol' name='idPrefix'/>
            <macro:param default='tabs' name='class'/>
            <macro:param default='false' name='includeBottom'/>
      </macro:include>
</div>

The yellow highlighted value is the number of widget you want to save side-by-side. The code present in a default Blogger template supports this value till 4 widgets side-by-side.