Found the problem. It's in your font size of 4 for the month. It should be 2. That is set to "strdefaultfontsize" in line 31 of "cal_functions.asp". So I assume you've either made your default font size larger or that line has been changed. If you want your default font size to be 4, then change that line to one of these:
"<font face=""" & strDefaultFontFace & """ size=""" & strDefaultFontSize-2 & """ color=""" & strCategoryFontColor & """>" & MonthName(Month(dateToDraw))
or
"<font face=""" & strDefaultFontFace & """ size=""2"" color=""" & strCategoryFontColor & """>" & MonthName(Month(dateToDraw))