Although my mother is Jewish, I did not have a bris (my parents were not observant). Should I decline full participation in services such as receiving aliyot until I have a bris milah?

The question should be a theoretical one (it is discussed in Tzitz Eliezer XI 9, Sridei Aish I 11 and Iggrot Moshe Orach Chayyim II 33) because you should not delay your brit milah for anything but serious medical reasons. It is time to rectify the wrong.