If you don’t want margins of other pages to change then you could try this code on your about page:
<div id="myabout" style="margin-left: 20px; margin-right: 20px;">
<------- Put or copy/paste your other code here ------->
</div>
The first line is self explanatory so you need to change the first line margin of 20px to whatever you want.
Good luck.