I've dug a shallow grave, what am I doing? In over my head..

[LBlala]

I've spent a sort of obsessive amount of time on here trying to find similar questions to mine & answers, but finally thought I'd post my 1st forum post in my life (self sufficiency broke me, gave sore muscles)..Sorry for the length, I couldn't seem to be concise...

I live in a rented 150yr old row-house in Washington DC. I attempted containers last year/my 1st yr at this house (I thought I might move & somehow take em w/ me), & failed. It's hot here, like 90-105 ave summers? They often needed water 2x a day, & I was terribly inconsistent (I thought, but looking back could have just been the top 2" were dry).. I didn't know about 'details' like fertilizing, self watering pots, shading, pollinating (anything). I got a weak few tomatoes, blossom end rot, cracks, dropped fruit, all of it, I wasted a lot of money on soil, etc... BUT, I learned!

THIS year, I researched (a LOT), dammit, & want to do it RIGHT! So glad to have found this resource.. I live for tomatoes, & want to make em the best little growing ground I can. But, I have dug this shallow grave, & am freaking out & wondering if this was my Worst Idea

So here I've got a hole in my lawn 6 ft long, 3.5 ft wide, & 2 ft deep. The pics are from early on. The boyfriend (dangerously supportive of my poss insanity) & I dug it w/o any fancy tools. The reason why is bc everything except the already-amended strip on the side is solid clay, just a mess. Rain it just pools up, and when it's dry it often cracks & is like dry cement.
We've found a bunch of rusted up ancient things, rocks, etc down there... . I had this idea I'd have a long strip for like 8 beautiful plants (some beefsteak, some sm-med) with lots of fruit & that the roots would need room. We're willing to keep digging it longer for more plants 24 ft, but need a plan for what to do next, & MOST important, is it insane/necessary?

What now: keep digging longer & go with it? Fill it up with the same dirt & call it "double dug"? Fill it w/ what instead? Chem free grass clippings? I don't have much homemade compost, but can buy things.. Btw I have around the house gypsum, tomato tone, perlite, vermiculite, can get sphagnum peat.. (I have potting soil but that's not right I know)... Should I get the wood/type sides (like my neighbor's healthy 50+ yr old garden)?

Btw, I'm still boggled that med/large varieties can grow 2/earthtrainer... but the pics show it so I'm building one too, just need the fabric.

Thanks for your time, & advice!