1. Can I say ‘it’s an honor’ kind of exaggerated? In that phrase?

if this is something going on in IG and you're setting things straight then you can say something like:

it will be MY honor to clear things up. (sarcasm or exaggeration is conveyed in capitalising)

2. Do you also mean only ‘just’ can mean to arouse desire?

No. In this context Just is like also 'It's also about'

So, if you're getting people saying things about you being sexual and you want to clear it up:

This isn't only about my body.

3. Can I say ‘ I want to share a healthy diet and life style as a positive way? Because I have no idea why you put ‘to’.

Yes. but change the last word positive way to positive thing.

I hope this helps

English composition

I don’t think I can stand it by not (stand it = the ability to continue with current situation)without making a post on IG. It will be an honor(word usage not exactly right here. If something is an honor it is something given to you. Something asked of you that is proving your worth or morally upright. Eg; asked to perform a solo. 'It's an honor' given an award 'it's an honor' invited to be a bride's maid 'it's an honor')

Perhaps: I am proud of myself. ( you are proud of your achievement)

But I don’t mean just the showing off like sexually(just and sexually implies that you want to also arouse desire for sex in another). If this isn't what you mean then: But I don't mean to show off sexually.

I want to share it as a positive way as sharing to a healthy diet and lifestyle.

Please post a correction so I can see if I'm close to what you're trying to say.