printf is your solution.
netstat -an | grep tcp |awk '{x[$6]++;} END {
for(i in x){printf "%s ",i};print "";
for(i in x){printf "%s ",x[i];print ""}
}' |awk '{printf "%15s%15s%15s%15s%15s%15s\n",$1,$2,$3,$4,$5,$6}'
15 is the size you want to apply to each field.
Good luck.