Reading past threads it seems submitting an LOI doesn't change your position on the waitlist, nor will anything. They seem to use a grading scale with a score that sets your place on the waitlist and this score cannot change, however showing interest in the school (such as an LOI) will show more of an interest in comparison to other applicants in the same score range as you which in turn will increase your odds.
I am in the exact same boat as you, and I suggest keeping in contact with UCF to let them know your situation. Communication is key and as long as UCF is aware of the position you are in, you should have nothing to worry about. Good luck, and hopefully we both get off this waitlist sooner rather than later.
I hope to see you there