I went to join a cata group at lvl 6, and they ended up clearing the maze, and I ended at lvl 11.

I thought this was great, untill I went into the arena and tried to kill some lvl 11 monsters, which didn't go so well

Is this just my gear being to outdated, or is my build wrong or something?

I went the first 10 into vit, and the rest from lvls into str. I'm using a rare II axe, and some other random stuff, mostly II.

If I upgrade to lvl 10 gear should I be able to kill lvl 11 mobs fine?

Ty for any help! Btw I'm very new to LS

Yes, if you can buy a level 10 weapon with 60%+ ee you will kill A LOT faster

Heres a nice guide that might help you out http://forums.d2jsp.org/topic.php?t=43961870&f=276

Feel free to PM me if you have any more questions. Good Luck!