Matching Crystal Reports with Windows Form

I am writing an application that outputs some text to a crystal report. In simplified terms, this is what happens...

The crystal report contains a textbox which is fixed in size (both width AND height - this is the way it needs to be).

On the windows form I utilise a RichText Box to take the user input.

I need to match up the RTB and Crystal Reports box. I know its not going to be perfect but I need it to be as accurate as possible. I currently have the rtb width roughly equal the Crystal Report box width and I use programming to count the number of lines in the RTB. The application already knows how many lines it is possible to get in the Crystal Report and hence there is a line limit on the user input. However, there are some situations where words can move down a line when it is displayed in the crystal report as opposed to the RTB, mainly because it is an approximate. I hope this makes sense!

This is rare, but it has happened.

Does anyone have any suggestions as to how I could improve this or other ways I can go about acheiving this matching

Thank you in advance.