Howdy tammylfinch,
Is it possible that one of your date time settings is not configured how you would expect? There are two different settings that are considered when deciding which day to display an event on.
The first is your WordPress’ timezone. This can be changed by going to WP Admin > Settings > General, and scrolling down to Timezone. Is it configured as you expect? It sounds like you want to set it to the UTC CST, which I believe is -6. Is this option correct?
The second option is found in WP Addmin > Events > Display. Scroll down to “End of day cutoff”. Is this set to midnight? If not, it sounds like you probably want it set to midnight.
Does that make sense? Did one of those options fix it for you? Please let me know. Cheers!
– Brook