You are voluntarily here and finding common ground with an ADHD meme. If you've felt like there's something different about you and have been waiting for a Sign, this is it.
Just keep an open mind, since a lot of different things can cause ADHD like symptoms. "I actually don't have ADHD" is also important information, and a good psychiatrist or therapist can help guide you to wherever the truth lies.
I've had a feeling that I might have it for a while but idk what to do. It seems like there's probably not a sureshot way to know I have it? And if I don't, it'll always feel like an excuse to other people.
Talk to your doctor and/or psychiatrist and they can't test and diagnose. Even being diagnosed, I still often feel like I'm just making excuses when something stems from my ADHD, but it's important to remember that it's not fair to yourself to downplay your own challenges. Acknowledging the challenges you face, and their affects on your life is not making excuses. It's being honest with yourself about what you experience.
Also I have one question. I've always done reasonably well on exams by cramming on the last day (more like last night) when the pressure is extreme. That doesn't take away from the fact that I could have it right? Like I'm good at cramming something under pressure and vomiting it out the next day, but am also awful at something that would require regular periodic studying.
Sorry for the late reply, but as the other commentor pointed out, what you described is incredibly consistent with ADHD. There is a reason we are prone to procrastination! Definitely talk to your doctor or psych about what you experience.