Me and my gf had anal sex. got her period 3 days early & last 3 days only and the blood was dark red and brownish everyday? is that means pregnant?

A very tiny chance: Women have more than one hole, but sperm must enter the correct hole in order to swim to the egg and create a pregnancy. Any activities in the wrong hole do not lead to pregnancy (unless other activities happen "in the heat of the moment"). One can consider using a reliable form of birth control if not wanting a baby, regardless of what sexual activities are going on, as life can be surprising.