The problem of duplicate outputs is due to a single line matching both its own number and the $1 != 26 condition in the end. A simple solution is to add ; next after each prt(…) call.
The problem with zero outputs is likewise due to the $1 != 26 matching too much. You could, for example, add additional conditions to this line (such as $1 != 26 && $1 + 0 > 0).
These changes should produce the desired output. Other than that, the script has a lot of redundancy that could be optimised (e.g., all the { prt(1,1); next } lines could be merged into one with a more complex condition), but that may not be worthwhile for a one-off script.
edit: For example, this could be a complete set of pattern lines for this example:
/D Format/ { exit }
!($1 ~ /^[1-9]/) { next }
$1 == 26 { next }
$1 == 11 { prt(180,3.141592653589); next }
{ prt(1,1) }
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solved awk – restricting area in file, printing