Hi DV thanks for your post. Unfortunately it's currently not possible to fully justify text in Lucidchart, although the is a centre alignment option in the Alignment options menu above your toolbar:

However, we’re very interested in your feedback and committed to continually improving our products. If you’re willing to share, we’d love to hear more details about your use case or what you’d like to see in this experience within this thread. I’ve also converted this post to an idea so that it’s visible to others within the Product Feedback section of the community - from here, they can upvote it and add details of their own.
Finally, for more information on how Lucid manages feedback via this community, take a look at this post:
If anyone else has questions about text styling and formatting I recommend checking out our Work with Text article for more information.