How could I show someone that I'm 100% into IB?

In your opening paragraph, you very much come across as a hardo, but coming from a similar background, I have a few suggestions:

1. Dont come across as too serious. I know this is difficult because youve spent a lot of time building up your skillset and you may feel like you have a chip on your shoulder due to your relatively below average GPA (from an IB perspective) and coming from a no name university. I say this because that was how I felt. 

2. Complementary to #1, focus on connecting with your interviewers. If you hustle hard enough, you will land interviews, and when you do, it is important to focus on making a connection. When I was in your position, I tried to show how much I knew in interviews (e.g., talking about deals I'd read about, models I'd built, even getting into LBO Senior Debt vs. Mezz debt EBITDA turns). This totally backfired. It resulted in more challenging technicals coming my way, to the point where I faced questions I didn't know the answers to. Learn from my mistakes and come across as someone who is really interested in the M&A world and as someone who is easy to connect with and someone who is supportive. 
3. Hustle, hustle, hustle. Hit the LMM space. There are plenty of IBs out there that few people target, start your outreach there. Reach out to all alumni (I assume there wont be many), and then target local banks in your area (or neighboring areas). It will be hard to get people on the phone, but if you cast a wide enough net, some will respond. When I was in a slow period, I would jump on the phone with anyone who asked. When my schedule was jammed, I wouldn't even be able to respond to alumni other than to let them know to follow up in a month or so. 

4. Learn from your mistakes. Cold networking is brutal and it really is about coming off as likeable, so do your absolute best to form a sincere connection. No one is going to hire a non-target mediocre GPA student because of your background, and even if you are extremely intelligent, you are new to the "real world" so this will be discounted heavily. When you get hit with a question you don't know, acknowledge that you aren't sure, but explain your thought process and come up with a best guess. 

Lastly, if you are anything like me, you don't know what the hell you want. You are too young to realize this, but I too was dead set on IBD. Then I got into the space, didn't like it as much as I thought, and have since switched industries twice. You can by no means say you want to make it to MD until you are at least a Assoc 2, because then you really have enough exposure to IBD to understand what an MD does and to have "paid your dues" to the point where you are tough enough to have made it far enough up the ladder to actually survive to MD. So many individuals state they want to make it to MD at your age and every time it sounds absurd. It is like being in 8th grade stating you know you want to major in Finance in college and then go work at a hedge fund. Yes, some people have always known what they want to do and stick to it, but the problem is that 99% of the people who say this sort of thing do a complete 180 and end up on a very different path. I don't mean to sound condescending here, but I said the exact same thing, and left IBD after a few internships.