How to get in the right mindset?

I used to be a kid that did not have any features that were considered beautiful. I had glasses too small, hair too short for me, chubby face, no makeup never, and my features were a little bit different, i was 15. I remember feeling ugly.
Now it has been 3-4 years since that time, just turned 19. My looks have changed a lot. I do not wear glasses anymore and I have long hair. My features match more now together and they just look different than back then etc.( You know I grew out of the awkward stage.)
It is so hard for me to still think I am beautiful. I can't let go of the past and I am constantly thinking people still see me as that "not so pretty girl" . I am like somehow captured in the mind of myself back then and it makes me believe that I am too ugly for anything even tough I am not.
What can I do?
How to get in the right mindset?
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