So many things hit here- yellow tomatoes are little to no acid. Roma and plums are thick fleshed/bodied and are ideal for sauce. When initially making sauce, you should add all the extras, not after you can. Who ever said taste while making- yes sir, spot on. I feel like it can still be saved but you're going to have to be patient and figure out whats going to work in that and write it down so you can repeat the process.