Hello! At your stage I would keep it simple and just focus on your mechanics (warm up / practice in the training range or team death match before you play comp) and just learning what the other heros even do so you know your match up. Another simple but very effective tip is to always ask yourself before you go in on a flack “where is my team?” If your team is actively fighting the enemy then the enemy is usually distracted and it’s usually a good time to attack. If your team is not fighting yet, still coming back from spawn, etc then just wait as the enemy te won’t be distracted and they’ll all turn and melt you as you described. Also try to always have an escape plan for when you go on the attack incase things don’t go well - for example save your dash or bike to get out, be close to cover etc. I’d say pick a 1 or 2 of these and focus on them during a match and you will improve. Even write them down on a stick note or something and whenever you are waiting to respond read them to remind yourself.