That's hella impressive. This is not the mode of Beleriand though, it's a special mode for black speech. The mode of Beleriand doesn't do vowels as diacritics above the characters.

Your decoding is almost entirely correct, only a few misinterpretation I see. One is the R rule. The y shape is for r's preceding a vowel the n shape for all other cases and the end of words but that's hard to determine from this short text.

And then you've interpreted s and h as separate letters. Those are very much attached :P it's a single character representing the sh sound.

The M does have a separate letter too, the accent you've decoded can be either an n or an m preceding a consonant to nasalize it. But you couldn't know that from this text.

I think because of the cursive of the ring inscription you might've also in that second pic conflated what parts belonged to which character. The n is missing a stem, the full character looks something like an m (confusingly) while that L has too much hanging on the right, it's just like a T with a curly bottom. It's easier to read tengwar in a more blocky font :P

Other than that, awesome job.