GMAT Sentence Correction (SC) | Help needed in understanding modal auxiliary verbs

used to + 1st form is used to show the regular action of past.

I used to go to school with my friends
(now I don't go)(it is not a question if I was comfortable or not)


However, be/get+used to +verbing ==> when you start feeling comfortable in doing some action(verbing).

I used to perform in my school, but I did not get used to performing.

When I was a child,
==> I used to perform--first part
==> but I never felt comfortable in performing-- second part

Another example-- Initially,
...

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