Student or Learner
is it correct if I say : "I used to look like really ugly."?
"I used to look, like, really ugly!" could work if you are a valley girl. I'm guessing you are not, so you should leave out the "like": "I used to look really ugly." You can also use "like" if you are actually comparing yourself to something or someone: "I used to look like a really ugly frog" or "I used to look like Tom Cruise... in 'Vanilla Sky' after the accident."
: to have an appearance that is very similar to (someone or something)
: to resemble (someone or something)
▪ You look just like your mother! [=you resemble your mother very closely]
▪ That powdered sugar looks like snow.
look + adjective
▪ He looks angry.
▪ Her new haircut makes her look young/younger.
▪ That cake looks delicious.
▪ “How does the situation look (to you) now?” “It looks pretty bad/good.”
▪ It looks dangerous/unlikely.
Merriam-Webster's Learner's Dictionary