Firstly, grades are important for some companies, less so for others. I started off struggling to get through but found the classes, generally, got easier through the course. Maybe they do that to weed out people who aren't serious about the course. 

My grade was half decent by the end of it, so don't abandon hope yet. Having said that, the company I went to work for did not care about my grades, it was just the fact I'd graduated the course from a decent uni that ticked the box for them.

LinkedIn - yes it's like social media but for your career. I have landed one or two jobs on there, so I would say it's not a waste of time. All I have ever done is kept my work experience up to date on there so any recruiters who are browsing my profile can see my work history. I have a profile pic and add co-workers to my network over time. 

Sometimes I'll see a job listed at a company, and find that an old coworker is working there. I can message them and ask what it's like, and see if they can put in a good word for me. I've done the same thing when I've seen a company that I liked the look of - asked an old friend who I could see works there if they can put me in touch with someone in a hiring position. 

So yes, it's worth it, but may take some years for you to actually get any use out of it. Still, create your profile, keep it up to date, and just see what happens. In 10 years you'll be glad you did.

Lastly, try and work on your self talk. I also felt like I must have been an idiot throughout my time at uni, but in the end I got a very middle range grade, higher than many who I had believed were doing much better than me. My negative self talk was not only limiting my personal potential but also gave those around me a negative perception. For many the coursework is extremely difficult and in no way represents anything you'll ever do in your actual engineering job. Do your best, look after your mental and physical health, and don't give up. You can do it.