I think your 3rd rep may have been the best. My suggestion, change how you set up. Be more deliberate and practice getting tight in the starting position. There’s just too much movement going on at the bottom and you lose tightness as soon as the weight starts to move.
- Squeeze the bar hard.
- Flex your lats.
- Squeeze your ass like you’re trying to hump the bar.
- Hold the rep at the top for a 2 count.
Biggest and first thing to address, hold the lock out as soon as you get to the top you’re already going back down. Squeeze that ass, hold, down.
Doing that for 6 weeks should provide some growth, nothing is overly wrong, it’s not perfect but who cares, it likely never will be. Also maybe get a belt that’s wider in the front vs that older body building style belt.