first: Congrats!
unfortunately, you are in preseason so no rewards.
there are 10 placement matches. depending on how you do in them you will be placed.
It very much matters in which order you win/lose as well.
the first games weigh heavier on the placement scale.
if you win your first 5 and lose the rest you will be placed substantially higher than if you lose the first 5 and win the rest.
All that said, even if you were placed back into bronze, you'll get back to silver in no time.
You are already playing above bronze level, which you proved by leveling into silver.
you'll have no prob getting back to your current level no matter your placement!
Good Luck!