A bit late, but watching the vid now.
At the start before the fight begins 0:14 you bubble to farm energy from Junk, which I think is really good. Before teams go in and engage you usually have a “poke” phase where teams shoot spam damage at eachother, to get lucky kills, break shields etc etc. Using your bubbles selfishly here is perfect. Keep it up 
Around 0:28 you miss the Junkrat flanking your Moira. Remember that on defense you can control flanks with Zarya really well with Right clicks to farm ult and make them back away. When your Rein isn’t being actively pressured by their frontline, you can try to throw a glance at the flank routes on this map, which is usually left side. I think you could’ve bubbled anything there, ideally Moira but even a bubble on someone close by here would’ve given you 40 extra charge to punish the flanking Junk. Good timing on the self bubble when Hammond slams.
You were struggling with tracking the Junkrat at 0:35 and that’s normal, he was moving randomly and no one expects perfect tracking at your level. One thing you can to with Zarya to help you out at the start is to hit them with your right click. You can aim at their feet and the splash damage will send them upwards in a predictable trajectory making it easier to track them. Not to mention it’s a combo that puts out insane amounts of damage.
This is more of a general advice. But from the start all the way to around 0:40 when Ball is on point, you’ve been standing in one spot, out in the open for quite some time. I think this is one reason you find yourself dying on Zarya more than you do on D.va. D.va’s panic button (her shift) is much better at getting away from danger than Zarya’s personal bubble. The personal bubble is just some added tankiness (200 HP) you can use while retreating or engaging. Try to make a habit of using corners and walls to protect yourself. It’s really important to do so on immobile tanks.
Another thing you can work on; stick to one target especially with your laser beam. At somewhere around 0:33 you move your crosshairs sporadically between Junkrat, Mercy and Rein’s shield. It’s not an efficient use of your ammo and you minimize your pick potentialt. What I would do here is just focus all my attention on Junk, he has no sustain or escapes the same way Mercy does. Pick a target and rain hell on them 
0:47: Love the bubble on Symm. You already had decent energy and decided to peel Symm here. Following that I like that you take space later pressuring D.va and the Ana, and then retreating back to your Rein. I would’ve pushed the Ana and commited for a kill, but knowing your limits is good.
Nice kill on the Junk at 1:15, dude. You had charge, he was out of position and you punished him. If you get better at taking advantage of these opportunities you’ll improve on Zarya fast.
Now to 1:20 where you lose the fight. I honestly think if you had your team to play aggressive here with you, you’d be able to kill all of them. But he’s off doing god knows what. But no point in reviewing your team mates. What you could’ve done here is to not waste your self bubble. You were essentially full HP with no one hitting you and had decent energy. The Junk made a smart play to punish you for it here. Another way you could’ve played this better is probably sticking close to your Rein, EVEN THO it’s the wrong thing to do. You want to be aggressive, but you’re not gonna have aggressive Reinhardts in Gold. They play very safe and hold shield.
1:57 : Grav wasted here. One difference between D.va ult and Zarya ult has a tendency to be more team dependent than D.va ult. Meaning it’s only successful if there’s decent follow up. I think this was a bit of a panic ult. Things you can watch for before graving is; do they have a shield? If they do, you’re gonna need your team to pressure it with you, or have your Rein swing into the grav. You can make a solo play with grav, but you need to be high, preferrably full health and with your self bubble. This ensures that you can out damage the healers sustain. I have zero clue how you guys turn this fight around
but you did. Nice.
3:03: Another example of positioning that can be punishable. You’re out in the open. Granted you do have your bubble and for some reason you’re full health (what is the enemy shooting?!?). But make a habit out of staying behind cover or shield. The team fight isn’t on yet and you can spam right clicks for damage from a distance.
Man this is a lot of text. I’ll stop here so you can decide if you want more or not
Hope it helps
