The prototype of sitting is seat sitting (making ... sit).

The sentence you quoted, sit, is a sitting state, for reasons similar to worry, ... because there is just now in the stem, you should use the general past tense instead of having done. Besides, it is unreasonable for you to fill it like this. Sitting is the "completion" of doing, and people can't "sit down".

As verbs, 1.seat and sit can both mean to sit.

(1)seat is a transitive verb, which is more formal and often uses passive form to express active meaning. For example:

He sits between Jack and Tom. She sits between Jack and Tom.

Please sit down. Please sit down. ) Please sit down.

(2)sit is usually used as an intransitive verb and colloquial. For example:

The students are sitting at their desks.

Please sit down. Please sit down.

2.seat can also be used as a noun (while sit can only be used as a verb). The common phrase take a seat means "sit down". For example:

Please sit down. Please sit down.

Seat nouns. Seats. Have a good seat. The seat here refers to the place, not the chair. Please sit down, please sit down, please sit down. The following sentence is very common in spoken English and movies: Is the seat taken?

Please sit down in three ways: please sit down. Please sit down. Please sit down. (more polite) test site: the difference between seat and sit as verbs sit-VI；; Sit someone down.

Please adopt it in time if it is helpful. Thank you.