Is it normal for my operated lazy eye to look lazy only in the mirror?

No. If your eyes don't look straight when you look in the mirror, chances are its probably not straight at other times either, although i don't know how you would know unless you ask someone else and they may not be looking as closely as you are...
Not really. It may be that you are looking critically at yourself, while others are not noticing what you are seeing. If you and a friend look at yourself at the same time, and your friend does not appreciate the appearance of lazy eye, it can confirm it for you.