I thought about telling someone "You're most welcome, and accepted." Should I have said most welcomed instead of welcome?
In American English (and British English so far as I know) the idiom is "You're welcome"
you're welcome idiom
used as a response after being thanked by someone
Saying "You're welcomed" sounds strange and only makes sense if you're describing the actual process of being welcomed to someone in the second person, for example in the sentence: "You are welcomed into the house by your host".
I should say, I've never heard anyone use the additional "and accepted" part of this phrase. In the US, at least, the phrase is just "You're [most/very] welcome".
The answer is no - the way you said it was correct. In the phrase "you're welcome", welcome is an adjective (https://www.lexico.com/en/definition/welcome). Saying "you're welcomed" would be as weird as saying "you're talled" or "you're beautifulled".
Language, especially the English language, can sound very strange. Further, because something is popular doesn't mean it's correct.
To say "you're welcome" is poor grammar. "You're" is the contracted form of "you are". "You" is the subject and "are" the verb.
Now, in the case of "welcome", the actual verb in "you're welcomed" is "to be welcomed" making "are welcomed" a present participle. "You are welcomed" is, indeed, correct.
One doesn't say "you're honour" or "you're love" or "you're stupid" (😁).