This might help.  The following image illustrates your problem.  With the font size you’re using and with the default .5″ tab stop, at some point the numbers are going to bump too close to the tab.

Make sure your ruler is showing. 

What you can do is adjust the tab stop slightly to accommodate the larger number.  Select all of the lines that you have tabbed.  If this is difficult, click at the first line and then shift-click at the last line so you don’t have to scroll.

Visually determine where on your ruler you’d like the new tab spot to be and click.

Your numbers should now have more breathing room.  When you create a new list, it’s easier if you set the tab first.