streachmarks and weight

hi im 14 yrs old . im a girl. I am skinney at 5ft 5in but I weigh 134.5 is that healthy for me? I also am afraid to wear shorts because I have streach marks all on my thighs since I was 11. I think if I do wear shorts someone will see them and tease me…is there a way to make streach marks just dissappear? please help me… I will be so grateful.