You may have resized it when it was not in edit mode - that will do very odd
things to the fonts. You need to double click on the chart and resize that
way. If you do not want the font size to change as you resize the chart, make
sure autosize is turned off for all areas of the chart (it's a check mark
under the font tab).
If you are a "creative" and used to working with Illustrator or the like,
you'll be disappointed to learn that PowerPoint older than 2007 does not
provide kearning tools.