You do not have to submit your essays at the same time that you submit your Apply Texas application. You can log back into your account on Apply Texas and clicking on the my essay tab.
From the Apply Texas website:
***At the time you submit your application, you will have the choice to SUBMIT all saved essays with your application, or to submit each essay individually later via the My Essays tab.
Here is a page from Apply Texas regarding essay submission and formatting.
https://www.applytexas.org/adappc/html/faq_essay.html