Tips for Placements (new acc)

I started league may last year. I've never made it above B3. On this acc, I just made it to lvl 30 and im doing my placements. I did 6 so far, won 2 lost 4. OP.GG said my MMR is at Silver 3 right now which is good enough for me but how can I maintain that? I'm not used to playing at such a high elo. I'm a diana main, I'm used to playing with bronze people who can die easily so I can get a snowball started.

For example, In my last game, I was against an Aurelion. I got to level 6 0/0/0, whilst the aurelion went 4/0/0 ganking top lane over and over. I couldnt do anything till 6, not even counter roam. My support took smite on accident, my jungler was at 30 cs in 20 mins and my adc spent his whole game flaming everyone else. Of course we lost.

I really dont want to go back into bronze, does anyone have any tips for my next 4 placement games?