Mp3 disc, ok. That explains why it's only showing data size.
If all else fails, you may want to open a ticket and send in your files so the devs can analyze what's going on with the incorrect calculation.

I think I found part of the problem. The Auto-conversion size calculation is wrong. The total burn size is really 717MB.

Here's the final page of the burn wizard




This is a "data" disk with MP3s, not a Audio-CD

Is there a place where you applied any settings (maybe in options)?
Does it show somewhere what the collective length of the tracks are (on or before that final screen)?

Version 4.1.16.1836

At the finale screen just before I click the burn button at the bottom it shows Burn:662.5MB (Avaiable703.1MB/703.1MB)
Yet during the burn it stops at 649MB then asks for Disk 2.

What version of MM?

If I remember correctly (it's been years since I burned a disc), size limitations for music discs are determined by length of total music to size of disc
and data discs (including mp3 disc) are determined by size of data to disc size. It is possible to burn up to around 80min for music (well beyond the standard 74min).
I don't remember what settings are available in the Monkey.

What are your settings and what does MM state the projected "length/total running time" on the disc will be after you add all the tracks?

For some reason Media Monkey will not burn more than 649MB to a CD even though I'm using a 700MB CD and CD burning wizard acknowledges it a 700MB CD. The files I have selected only total around 670MB. The burn process with start but once it reaches 649mb it asks for Disk 2. What gives?