I feel ashamed that am not yet baptized at the age of 18, should i?

No need to be ashamed. Just fix the problem. If you want to be baptized, since you're 18 you can go tell a priest you haven't been and want to be. It's my understanding that it can be done privately, but the best and quickest answer to this is going to come from him, not Yahoo Answers. Oh, and regardless of the reasons why your baptism fell through the cracks, it's not important now -- and you don't need to answer for your mom's actions. Just your own. Go talk to a priest.