The problem you're having with that is that the M is too large to fit the circle because of the glyph space that the character has above the letter. That exists to ensure an adequate space between rows of text. You have three options:
1. Choose a font with less glyph space above the letter;
2. Use a smaller font; or
3. Use a textbox for the M and a separate shape for the circle.

For the third option, insert the M into a separate, transparent textbox, then position it over the circle. Once you have them aligned correctly, you can group the objects so they move together.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]