THE shot!

Hello! 😂😂I know some people on eve are experience with birthcontrol for me that's not the case I have a new boyfriend and I really want to be safe this time I'm used to the pull out game but now that I look at it it's asking to get pregnant so I want get THE SHOT im 103 pounds what I'm scared of is gaining wait.. Will that happen? How can I loss it if it goes in the wrong place? And if you had to pick a different birth control for me what would you pick? &why? Please help! So confused