What a horribly familiar tale. I did my undergraduate degree at Imperial, and guess what? Nobody gave a flying s**t about undergraduates. I too was left to sort it out by myself with no guidance whatsoever. Imperial College is a dump, I wouldn't send my worst enemy there to do a degree. I had the worst 3 years of my life there. I served time. Like you, I survived, but only just. The best part of 3 years was cycling out onto Queensgate when I left, giving the place 2 fingers, saying "F** you" and vowing never to go back. I did go back, for the graduation, which I did for my parents. Never, ever, will I return.
On a more positive note, Masters. Yes, if it will help you do what you want. I know people who have done a Masters, got little from it and ended up doing the job they would have been doing anyway. A few years down the track it's an irrelevance, because it's all about their in-job performance. Conversely I know someone who did an arts degree, decided that it wasn't for her, she wanted to be a nutritionist and went the full BSc-Masters-PhD route. She now works at a University, doing research into nutrition and its role in non-communicable diseases for, amongst other organisations, the WHO. She couldn't have done this without the Masters en route.