Welcome from me also. Much of what you said sounds very familiar to me. And I agree that you probably can never really "know for sure". I have a few points to make why you should be comfortable ignoring that, if you wish to:
1. Everything Does change. Constantly. There are labels that used to apply to us that no longer do – I used to be a cashier and I'm not anymore, I used to be a first trumpet and I no longer am. Sure those are more tangible than something like "aromantic" but I only mean to show that if it ever turns out that you were "wrong" that doesn't mean that you were wrong to use the label. Since
2. labels aren't a select once at the beginning of the game type deal. They can change. They don't have to set rigid rules for how to live your life. They aren't boxes you make a home in, they are little decorations you put in the home you have (does that make sense?).
If you feel like the label could help you, make you feel more comfortable or help you connect with a community of people with shared experiences, then that can be all that's important.
3. We're not gonna be mad at you in case it turns out you're "wrong"! If you say in a week or a year or 10 years that this whole "aromantic" thing was completely off for you then we're not gonna be angry or anything. I'm not even sure myself if I'll always identify as aro, but it helps me now and it's very important to me now
4. I do get not wanting to come out in case people will think of you differently. I don't know your friends and family but I think you're right, they might see you a little differently for a bit but eventually they're probably going to realize it's just a tiny fact about you that adds to the person they already know. I also used to be afraid I'd come out and change my mind and have to come out again and people would believe me less (which is honestly such a mean thing to think they would think. I think deep down everyone would know life is confusing. you can't always know everything about yourself). Funnily this lead to me identifying as bi "to me safe" and having to come out again later because guess what! turns out I was actually right the first time. Wow.
If you really feel you're ready and you're maybe annoyed by the assumptions people make don't hold back on coming out just because you're not a million percent sure. You're probably never going to be