How to properly auto-populate Rich Text field when checkbox is checked?

Hello, I really hope someone can help me with this. 

Here's the formula I tried:
If([1099-NEC (Checkbox2)]=true,"<b>CONTRACTORS (1099-NEC)</b> <br>Company Name/Individual's Name:<br> Contractor's Address:<br> Contractor's EIN Number / Individual's SSN:<br> Amount Paid:", " ")

Using the formula above, it auto-populates the field when checkbox is true but it won't allow me to input text on the field anymore.

Basically, I just want to populate the Rich Text field with this format:

CONTRACTORS (1099-NEC)
Company Name/Individual's Name:
Contractor's Address:
Contractor's EIN Number / Individual's SSN:
Amount Paid:

I can achieve this if I use a regular Rich Text field and set <br> Contractor's Address:<br> Contractor's EIN Number / Individual's SSN:<br> Amount Paid: as the default value. The problem is that I have 12 of this field, and when I add those fields in the email body, it shows up like this:

CONTRACTORS (1099-NEC)
Company Name/Individual's Name:
Contractor's Address:
Contractor's EIN Number / Individual's SSN:
Amount Paid:
CONTRACTORS (1099-NEC)
Company Name/Individual's Name:
Contractor's Address:
Contractor's EIN Number / Individual's SSN:
Amount Paid:
CONTRACTORS (1099-NEC)
Company Name/Individual's Name:
Contractor's Address:
Contractor's EIN Number / Individual's SSN:
Amount Paid:
...

That's why I opted for the Formula Rich Text so it remains empty if the checkbox is not checked. If there's an alternative/more efficient way of doing this, please let me know.