Bogey is one shot over par and Double Bogey is two shots over par. You're right that +7 or +11 is pretty bad, but you can still get the achievement with those scores on a table or two.
You have to get a total score of under par on all the tables combined, so provided you do well on the other tables, a bad score on a table or two won't hurt you. I got the achievement with a +7 and a +9 included in my score.
Bejeweled 2 Complete!