Is it OK to have 9 tiger barbs in a 20 gallon tank?

I wanted to have a school of 7 fish, but I ordered 9, because I thought that maybe between shipping, and acclimation, one or two might die...well all of them lived! Good I guess, exept now, I have 9. Is that too many for a 20 gallon tank? They are the only ones in there. There's also a big amazon sword plant and a piece of driftwood...What do you think? Thanks!!!