My age is 16 years old and my height is 5 feet 1 inch and my weight is 55.45 kg i think i am fat because my weight is a lot comparing to my height?

Best to assess is through BMI or body mass index where you input your values and get a sense of where you are, a normal BMI is roughly 20-25, there are many calculators online. Your pediatrician would be also a great resource to discuss goals going forward.

Agree with Dr. P. Visit this site for calculating your BMI. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV and Covid vaccines. Wish you good health!