Its the same quality regardless of size i put in the script.
The file and the font itself is crystal clear quality ... observe:
I check the font and image... that's the font you are using since all letters match but Q is so weird...
On the other hand does your string have ' '(white spaces) , if it does try removing them and see what result you get.
Also try moving the drawing position of the font left or right 1 pixel and repeat for up down.
And if that does not help, gimme the source code. I did SDL for some time now and i had issues like this before.