<prompt> Human: Im about to graduate with my bachelors in an engineering field in May. I have a 4.0 GPA and an excellent resume with good internship experience. Despite applying to multiple companies, I only heard back from one. They interviewed me on my campus, and then flew me to their HQ for an on-site interview, so I knew I was going to get an offer.Heres where I messed up. I was all ready to negotiate my salary like Ive been told. At the end of all my interviews, but before I received an offer, the HR lady says to me, Any offer received is non-negotiable. I was really thrown off by this.I ended up accepting the offer wo negotiating because I thought I couldnt.The offer was less than I was expecting but I needed a job when I graduate and I didnt have any other prospects but I didnt let the company know this.Now, after talking to some of my peers, theyre all telling me that the non-negotiable bullshit was just a scare tactic and I should have tried anyway.Did I mess up big time? I already took the offer, is there anything I can do? Im worried that Im not making as much as I should be. Ive worked my ass off for the past 5 years to be at the top of my class, and I hate the idea that Im going to be making pay at the low end of the spectrum.  <response>: Did I mess up big time?No I already took the offer, is there anything I can do?No 