Do not live off of coffee and 3 hours of sleep, that's your only mistake right there. Take notes from your friend who is well rested - sleep 8 hours a day. Resting is just as important for your grades as studying. Do not let your mental health suffer while you're going through naturally stressful classes in college, you need to keep an even keel about your moods during this time which means taking the pressure off of yourself. Don't listen to your sister who said you won't last a semester, that is very rude and terrible of someone to say to anyone else. Prove her wrong, take it easy.
Everyone has a hard time in college because college is hard.
Your marks are fine. You just need to lighten up on yourself and not stress out so hard. Stressing less will improve your grades, I'm sure.
Get help from study groups, or help from your professors if possible.
Don't jam so much studying into short periods of time, take 30 minute study intervals throughout the day so you can remember more things.
Talk to your professors about any unsatisfactory grade and ask them what you can do to improve it or what it is you don't understand about a subject. That's their job.
Take it a day at a time. Do your best. Eat healthy, and get enough rest. Limit your coffee intake, drink more water. Eat smoothies loaded with bananas and healthy stuff in the mornings before class. Exercise or do yoga or calming meditation before class or during breaks between studying. How can you possibly remember anything you study if you're shaking and worrying at the same time? You can't. Use your creative juices with regards to every class you're in, and ask for help when needed.
By the way, stop comparing yourself to others. I'm 100% sure you're not the only one who got a 40% or a 60% in that class. The only one you need to be concerned about is you and not looking at other people's grades because that doesn't feel good to anyone. Even someone who got an 80% would feel like **** if they saw someone else get a 90%.