This comes up quite frequently and the main resolution I have seen is to hide that title and instead use a text box to hold the title. You can then set the width of the text box manually to ensure it is the right size for you. I would also recommend putting both the text box and your colour legend into a horizontal container, so that you can move the two around together later if needed.
I hope this helps. Let me know if you want me to clarify anything.
When You'll hover over on legends window or near legends color square, you'll see a thin line where you can put you cursor and drag and wide it. it'll help you to display the full title of legends.
Please let me know if it doesn't works for you but I'm **** sure it should works.
Please mark helpful if it works.