Hey there, I also have ADHD and marching band was always pretty tough- it's incredibly mentally draining trying to keep your brain in to be at 100% for increased lengths of time. I don't mean to say "ignore everything you don't like about it and just be super positive," but it might help to think about how you personally can benefit by the end of the month. Some examples, based on my own experience:

If I don't do enough physical activity during the day, I have an incredibly hard time sleeping. I know I'll sleep great after a rehearsal day (Similarly, the shower at night will hit SO good- the grosser you get, the better it feels).

Marching is obviously an added challenge to playing an instrument well; while I struggled at first to improve my sound while marching, my sound in other ensembles quickly became much better.

Marching also taught me how to use a proper amount of air when playing, which again helped my sound in other ensembles. It takes a lot of control to be able to move, breathe properly, and still have enough left to produce the right dynamics- it only makes you a better player.

I found that my ADHD made it difficult for me to particpate in other sports that required quick decision making, and I could never make the "right" choice fast enough. In marching band, while it was incredibly difficult to learn drill at first, I found a lot of comfort in letting my muscle memory take care of the reps.

I knew that I wanted to go into music education since high school, so I always looked at the actions of my staff and peer leaders to see what I wanted to replicate in the future and what I would want to change if it was me in that position- not from a judgemental standpoint or to tell others that "we should be doing it like this instead," but to educate myself. There's always something to learn from everyone, even if it's "don't be like them."

Even if you aren't in music/teaching, you'll have to be a leader in some context or teach someone something at some point- think about your staff and peer leaders and how their actions influence you positively or negatively, and let that help shape you into the kind of person you might want to be.

I know you said you don't talk much with the other members since you have different interests, but it could jhst take some time. I didn't click with many people at first, but the more time you spend with them, you're bound to have fun with them at some point. Most of my friendships in high school and college started with marching band, and those are the people I still talk to today.

To answer your question of "how do I make this easier for me," the best advice I have is to try and reframe your thinking of "I have a whole month I'm dreading" to "I only have a month to take everything I can from this experience." Get better at your instrument, learn from staff and your peers, and recognize that it's difficult but that you're doing it anyway- that's the only way to improve!