Question

Does it matter where you put the word "not" in a sentence? Would I say I'm usually not or I'm not usually? Also, did I use the quotation marks correctly in my sentence?

Let's assume that this is the complete sentence. "I'm usually not so late." You want the "not" near the "late" since that is what it modifies.
Regarding the quotation marks. You need to put one set at the beginning of the sentence and one set at the end.
Hope this helps.