SR would only be if the taxpayer or spouse were over 65.  so if it was not an  SR and the taxpayer or spouse was over 65 it's likely the wrong birth date was entered.  over 65 get a larger standard deduction. 

The 1040SR is the same as the regular 1040 just bigger type so it prints on 3 pages instead of 2.  When you efile only the tax data gets transmitted not the form it's on.   

Turbo Tax will automatically give you the 1040-SR if you or your spouse is over 65.

When you print it will print on the 1040SR even if you see only the 1040 on the screen.  You automatically get the 1040SR if you or your spouse is 65 or older.  In the Desktop program you can tell it which one to print.  

It is really immaterial as both forms are IDENTICAL line by line  ... except the  SR  has larger font and is stretch out to 3 pages. 

TurboTax selects Form 1040 or Form 1040-SR based on your age at the end of the year that you are filing for. For your 2020 tax return, if you (or your spouse if filing jointly) were born on Jan. 1, 1956 or earlier, TurboTax will print Form 1040-SR. If you (or both of you if filing jointly) were born Jan. 2, 1956 or later, TurboTax will print Form 1040.