I think this is an excel issue not a dynamo one. Excel handles numbers written as 20.00 as if they were only 20. So you either need to change the formatting in Excel so the numbers all show two decimal places, or in Dynamo convert the number to a string, remove unwanted extra zeros or add additional zeros as necessary and live wth not being able to use the string as a number in excel or on a return trip back to Revit.
If those options don’t solve the problem, please share a Revit file containing the annotations and your Dynamo script and I can have a look later.