You have answered it partly yourself..to stop this negative Thinking-Feeling loop. The way you think is the way you feel and the way you feel is the way you think. Most of us get stuck in this loop day in day out and sometimes for years. The same thoughts rush in when you wake up. So how can you possibly create a new possibility or future with this mindset?
Feel free to message me if you wish to discuss this a bit more. I have some mind management & meditation tools to help with this.
Preparing for MBB and Consulting in general is not easy. So, dont get disheartened as pretty much everyone experiences what you are going through. The key thing is to make a plan, believe in it, keep practising, celebrate mini sucesses, take regular breaks (step away for 2-3 days) and don't worry about the outcome. Give your best and let things happen.
What other people think of you (good/bad) only boosts/hurts your ego. It has no real existential meaning i.e. you still have to work and achieve your goals..its your life. Please don't get into consulting for the wrong reasons- peer pressure, money, impatience etc. Go for a career where you can be joyful and give your best. If thats Consulting, fantastic. Right things will happen in due course. Success & money will come.
Regarding PEI stories, feels like you are trying hard to think from other people's prespective i.e what will stand out to please them. Nah! Dig a little deeper into your school, uni, internships and personal life and you will have plenty of examples. You dont have to climb Everest but show direction to someone (could be your cousin) when they needed it the most. How you tell the story matters. have a look at this thread: https://www.preplounge.com/en/consulting-forum/how-to-start-an-answer-of-telling-a-story-about-past-projects-8188
Please also search the forum as there are plenty of threads and tons of tips on PEI.
One step at a time! Keep moving forward.