Renee
You can't auto fit the row height of merged cells.
When I have columns merged, which I try very hard to avoid, but sometimes on forms it is the only way to go, I will have column to the right that is the same width as the total width of the merged columns . In that column will be a formula that picks up the value in the merged columns and that cell will be set to auto row height, making the row the appropriate height for the merged columns. The best solution, by far is not to merge cells.
I hope this helps.
Ken