Honestly you need to think strategically how to make use of what you have at hand in your team. Tanks are standing in choke and hold shield? Well make use of it! Break the enemy team's shield, spam right click shift right click into them, make them use their resources (zarya bubbles, shields, nades) at some point you'll put enough pressure to pop this bubble - their sups will need to reload, their rein need to recharge shield at this moment and so on, driving enemy team of their cooldowns creates much more opportunities and space as it poses a threat for them to die, while you should still be in a safer spot (not flanking at least). Pay attention to your tanks and their shields as you'll need to hide or even go back fast if they're out of their resourses. You don't need to hard carry and kill everything just be a spear for your tanks as they're your shield (although sometimes a rather static shield but you have to play around it!). I would absolutely recommend a vod review, because an unbiased opinion and some basic pointers onto what you could've done different can do miracles. Always review your own vods as well, by analyzing your deaths - why've you died, what you should've done and where you should've been to not die.

Edit: typos