GNU screen: key to access tabs above 9

try to use
(C-a ")
Display all windows in a table for visual window selection. The desired window can be selected via the standard movement keys (see Movement) and activated via the return key. If the -b option is given, screen will switch to the blank window before presenting the list, so that the current window is also selectable. The -m option changes the order of the windows, instead of sorting by window numbers screen uses its internal most-recently-used list.
UPD.
You can use binding to access windows above 9. here is the link text

You can also use (C-a '), and gnu screen will prompt "Switch to window:", where you can enter as many digits as you wish.

According to screen's manual page, you can add the following lines to your ~/.screenrc file:

bind -c demo1 0 select 10
bind -c demo1 1 select 11
bind -c demo1 2 select 12
bindkey "^B" command -c demo1

makes C-b 0 select window 10, C-b 1 window 11, etc. Alternatively, you can use:

bind -c demo2 0 select 10
bind -c demo2 1 select 11
bind -c demo2 2 select 12
bind - command -c demo2

makes C-a - 0 select window 10, C-a - 1 window 11, etc.