Please help me

I joined in this tournament (https://www.chess.com/tournament/fast-39/pairings),i am really sure, but when the tournament started i wasnt in any round. Why?

You were below 1100 right before the start of the tournament. I don’t know if that was it.
I wouldn’t worry about it. You can join another tournament.

Yes, i joined in other tournaments, but i want to understand.

I joined in "fast" tournament and before the start i became below 1100, so am I out? 

The tournament’s rating range is 1100-1300.

You might have been above 1100 right before the tournament started. By then the tournament could have been full.

I was looking at your archive. You were playing in a tournament when this tournament started.

Non-premium members can only play in one member created tournament at a time. That rule doesn’t apply to official chess.com tournaments. See link.

https://support.chess.com/customer/en/portal/articles/1444843-how-do-membership-levels-free-vs-premium-affect-access-to-turn-based-tournaments-

but only at the moment i'm playing some games in 5 tournaments at the same time!?

It’s possible that they increased the tournament limit for non-premium members.

For a definitive answer, you should ask the company staff.

https://support.chess.com/customer/portal/emails/new

Last time I played in any tournaments I think the limit was three of four for free members. If it's been at one, maybe it didn't work if tournaments weren't filling up quickly enough for paying players to stay happy.

To withdraw from a daily tournament:
Go to play > tournaments with a browser. Click on the daily tournament’s link. Click on the “Withdraw” option.

If the tournament has already started, your ongoing tournament games will be forfeited.