Your Motion is essentially seeking "leave of court" to extend a deadline. The omission of "leave" in your Motion should not be an issue. Of concern to me is that you're navigating the world of Experts Witnesses in litigation without an attorney. You should speak with a certified Limited Assistance Representation attorney to see how he/she may be able to help you in a cost-efficient manner. You can basically hire an attorney to provide limited representation of you (drafting a document for you, arguing a Motion for you, or any other limited task) whenever you feel you need an attorney.
I hope this helps.
Omitting the word "leave" is no big deal. However, it may be a big deal that the deadline passed several weeks ago. Usual practice is to seek an extension before the deadline.
The above answer is provided for information purposes only. It does not constitute legal advice or create an attorney-client relationship.