You would probably be vaporized by energetic collisions with space dust. Ignoring that, and assuming that you travel in a geodesic "straight line" (like light does) and space is not curved, you will never return to where you started from. Scientists still seem to be unsure of the number of dimensions of spacetime, and whether the universe is expanding at an increasing rate or will eventually collapse to a Big Crunch. So I cannot give you a definite answer.
