I am having the exact problem everytime I work on projects for our clients.
Maybe somebody have a better explaination why DotNetNuke needs to add a class called "DNNAligncenter" everytime where we have a pane (in setting pages)?
The fix for it without overriding to the DNNAligncenter class is to set your table or table cell to left-align.
What I usually do is go to your main container that wraps around the site, specify left-align for the table or table cell, it should solve the problem.
Unless somebody has a better fix, please share.
i.e. #mainConatiner td {text-align: left;}
Hope this helps!