There are those who would disagree with you, oocc
The ‘matter in two places at once’ thing was an interesting plot device in Timecop, but possibly not very much more.
Suppose, for example, that matter is nothing more than little kinks in the fabric of spacetime; if this were the case, then there’s no reason at all why you can’t put a kink here and a kink there; - the kinks themselves would have no individually unique properties.
'K, I will chime in.
From a biological rather than quantum angle:
Your matter 7 years from now will not be the same as your matter now, it will have changed due to diet, chemical reactions, blah blah. So this would mean you wouldn’t be duplicating the matter on a cellular level.
Think about that for a minute, KingLupid.
True, you shed cells and grow new ones. But the atoms which make up those cells doesn’t change. They’ve been around virtually since the beginning of time. We’re carbon based, or so I’m told. Remember Sagan telling us we’re made of star stuff? 
Ever wondered why there’s no huge hole under a giant tree from the tree building itself from dirt, etc?
Maybe somewhere out in space or in the 11th dimension there’s a big bin of free matter, and when you travel back in time, the matter that creates you in that time period is borrowed from that bin of matter temporarily. So no matter in the universe is destroyed, it’s just moved. Of course, if everyone gets greedy, there’s no more extra matter for anyone.