Append to String Issue

Question

I am trying to make Adaptive Card Message Dynamically.
I am trying to append each of these values to a string variable X

----------

[
"phoneNum":"54654564564",
"email":"testing@testing .com",
"ageLevel":"Toddlers",
"schoolGrade":"",
"booksCategories":"",
"location":"Country Hills Library",
"numTitle":"",
"titleTypes":"",
"materialType":"",
"subjInterest":"",
"pastBook":"",
"numBookBags":1",
"bookBagTheme1":"Things That Go",
"bookBagTheme2":"",
"bookBagTheme3":"",
"bookBagTheme4":"",
"comments":"test",
"isSubmittig":false",
"wasSubmitted":false"
]

----------

So I used the Append to String Variable

My problem is, the final value of the string variable X is shuffled:

---------

[
"email":"testing@testing .com",
"phoneNum":"54654564564",
"isSubmittig":false",
"subjInterest":"",
"ageLevel":"Toddlers",
"schoolGrade":"",
"booksCategories":"",
"location":"Country Hills Library",
"numTitle":"",
"bookBagTheme4":"",
"titleTypes":"",
"bookBagTheme3":"",
"materialType":"",
"bookBagTheme2":"",
"pastBook":"",
"numBookBags":1",
"bookBagTheme1":"Things That Go",
"comments":"test",
"wasSubmitted":false"
]

----------

Please help, I have tried doing this in Flow but did not encounter this issue.