The simplest way to clear the extra letters is to have a set area of the screen that you are going to print the value to, say 4 characters in this case, then pad your string with ' ' (space) until those four letters have been written. For example:
char x = 0;
char y = 0;
graphic.setCoordinate(x,y);
graphic.setFont(Normal_SolidBG);
char numSent = graphic.print("123"); //prints the number 123. The print function returns how many letters have been written, so numSent=3
char oldX = x;
x += (numSent*6); //for normal size font, each character is 6 pixels wide
while(numSent < 4){
graphic.print(' '); //pad up to 4 characters.
numSent++;
x += 6;
}
x = oldX; //restore original print location.