I also added the answer to the lesson note.
But since I like your question a lot, I'm copying the answer here,too. Your question must be interesting for other students, too.
Yes, there is another way of writing "so." Please take a look at this site (just look at the three "so" in the rectangle).
The right one is the another way of writing "so." Both "so" is correct. But the right "so" is considered to be an old "so," and only the regular そ is taught at school nowadays.
Personally, I like to write "so" in the "old way." I think the old "so" is more beautiful!
Oh, I see! Thank you for your answer! I also agree that the old one is more beautiful. :)Chocobell
Commented 6 years ago