It should work the way you do it:
DigitScore: Set text to RegexReplace(str(score),"^(\d+\.\d)$","g","$&0")
or
DigitScore: Set text to len(tokenat(str(score), 1, ".")) = 1?str(score)&0 : str(score)
It looks like you append some extra zeros to the DigitScore in another event.