mRNA coding from RNA code?

I think you may be confusing DNA replication with protein synthesis. RNA molecules are not in long strands; they are molecules of ribonucleic acid with triplets of nucleotides on them only. In other words, for each triplet on the DNA strand, there is a single mRNA molecule for each triplet.

TTT would attract and mRNA molecule with an AAA triplet on it.

Then, ACG would attract a mRNA molecule with UGC (uracil replaces thymine on RNA molecules)

You move down the line like that, and then you seem to have found a table translating which amino acids are coded by which triplets but remember this; the code must be reversed first, as it is on tRNA molecules, not on mRNA.

Taking the first triplet again, this means that TTT would attract a mRNA molecule with AAA, but then it will be translated as UUU on tRNA, so that's the code you need to determine which amino acid the DNA molecule intended.

ACG becomes UGC on mRNA, which is ACG on the tRNA, which is the code for the next amino acid in the protein being built according to these blueprints from DNA.

You keep going on down the line, in triplets, so the next would be GGA=DNA, CCU=mRNA, GGA=tRNA, and GGA is the code you need to figure out the amino acid it codes for.

The bottom line is that RNA molecules are small, they are not long strands with 5' and 3' ends like DNA. They code for only one amino acid, each triplet being the code for a specific amino acid. Many amino acids (since there are only 20 different kinds in working protein synthesis) have several different codes that will code for them, so there are duplicates on amino acid tables for a given amino acid.

The mRNA molecule leaves the DNA as soon as it matches up its bases, it does not linger nor does RNA form long strands along the DNA; each RNA molecule is small and independent of other RNA molecules.

That's important for you to understand, because it seems that you've mistaken how RNA reacts with DNA during protein synthesis with DNA replication, which does not involve RNA at all, and is the making of two identical strands of DNA in preparation for mitosis, or cell division.

They are two entirely different processes!

Caitie, mRNA strands are long and do have 5' and 3' ends. The 5' end has a cap structure and the 3' end is a poly A tail. mRNA molecules are not three nucleotides long and do not code for one amino acid. They can code for hundreds of amino acids at a time.