difference between close and closely? Maybe 'closely' simply is wrong word?

[Eureka]

English Grammar Error, Intermediate level

ESL/EFL Test #20 "Singular vs. Plural Nouns", question 9

Now remember when you're travelling on the underground train, don't stand too closely to the doors.

(a) remember
(b) on
(c) closely

English Grammar Error, Intermediate level

ESL/EFL Test #20 "Singular vs. Plural Nouns", answer 9

Now remember when you're travelling on the underground train, don't stand too close to the doors.

Correct entry: close
The error was: (c) closely

You have not found the error.
Now remember when you're travelling by the underground train, don't stand too closely to the doors.
_________________________

Is there any difference between close and closely? Maybe "closely" simply is wrong word?

Eureka

[Conchita]

One of the meanings of 'closely' is 'in a close manner'. Now, what we need here is an adverb that modifies not the way we stand, but where we stand: close to, or very near (the doors).