Full universe at the scale we think of as "human-ish" would need fudging at the microscale and macroscale, full universe at the microscale is no doubt beyond any sort of efforts which don't include a line stating "a wizard does something here" to cover problems like the sim having to accurately sim the particles which need to accurately sim the sim simming the particles, sim sim salabim!
It takes a whole fuckload less computronium to reproduce exactly what you determine to be the real universe around you, your local neighborhood, your view of the internet, of distant objects, other people, etc, but I'm pretty sure it would take less energy and use up less matter doing that than you would need to actually send yourself over to just the next closest stars, never mind anything much further out.
I mean, assuming we're not allowing flight plans like "coast on a trickle of laser energy from solar arrays on mercury until we hit a fraction of a 1% of the speed of light and reach our destination so far in the future that it is no longer the closest star and hasn't been for kiloyears" which would be much cheaper in terms of energy/matter costs.