No. numbers 2, 3, and 4 require the genitive singular.
The genitive singular ending for neuter nouns is "-а".
Additionally, the nominative plural ending for neuter nouns is also "-а", so "Окна" is a very regular plural as well.
Probably a bit late, but it is on the letter а. One way to tell is that when you hear окна you can tell the o is pronounced as a. This is because unstressed o is pronounced as a.
I wrote the number 2 and it declined it, i think we should be able to write the number instead of spelling it
That idea misses the whole purpose of this course. Learning a language means to obtain the ability to read, spell, pronounce and understand both words and numbers. Even the exercise is called "Time&Numbers"