There is no way to opt out. However, in the Review section, you can put 0, in the box up top, or leave it blank. Either one should work.
You need to go into it to correct it, and it will popup a form where you can enter a '0'. The corresponding boxes should be highlighted in yellow. If you enter a 0 into a yellow box and it turns red, then you need to delete the 0 and leave that box completely blank.
This is just one of several bugs within TT.
You are not required to defer the self-employment tax. We understand your experience.
Go back into the program: Be sure to put zero in for the amount if you do NOT want to defer.
The self-employment tax on that portion can be postponed for payment in the following year. You can postpone that portion of your taxes due with no penalties or interest, if you qualify. If the program is saying you do not qualify, you must be getting a refund.
You might also have a piece of data stuck, you may want to clear cookies and cache or change browsers.