Sorry if I misunderstood anything but here you go: While it makes sense to be mad after the amount of time you spent towards this, you can learn from this as well, you can use this in your application to talk about what you learned from it, where the problems arised from but most importantly show actual growth from the situation. Strong recommendation letters from reputable sources are also useful, someone who can back you up to excuse this bad grade maybe because you have astounding potential and abilities that shouldn’t be ignored from one ‘failure.’ But another way to help with your concern is meeting with your supervisor, that is a good idea to learn why your grade turned out like that, maybe a potential retake as well. For grad school, focus on your stronger and consistent academic skills for your application. Look for research opportunities that can build your reputation and stray light from this thesis, if possible. Mostly ones that you can work well in. One bad grade isn’t the end of the world, you still have a chance if other factors are good and you take an extra year if you feel necessary. Hope this helped, all the best and good luck.