So you want a five-column layout with fixed widths for your columns? Do you not need a margin in between columns?
If you read the documentation in your Dashboard > Appearance > CSS Settings > Choose CSS Grid, it says that you can create custom widths, but everything, including margins, have to add up to 960 pixels. Right now you have 955 px, so you're 5 px short, unless you intend to add some spacing in-between your columns with a margin.
So one example would be to add this to your index.php (note 5px margin to left of column 3 to make total width 960 px):
Code:
<?php get_header('Foo'); ?>
<div class="row">
<div id="widgetarea-left" style="width:100px">
<?php dynamic_sidebar( 'Widget Area LEFT' ); ?>
</div>
<div style="width:200px">
... Column 2 ...
<div>
<div style="width:335px;margin-left:5px;">
... Column 3 ...
<div>
<div style="width:200px">
... Column 4 ...
<div>
<div id="widgetarea-right" style="width:120px">
<?php dynamic_sidebar( 'Widget Area RIGHT' ); ?>
</div>
</row>
<?php get_footer(); ?>
This should give you widget areas to the left and right, called Widget Area LEFT and Wdiget Area RIGHT when you go to Appearances > Widgets.