First, make sure your rifle is straight up and down and isn't canted when you're firing. If it's consistently off to the left it could be that you're canting it (if you're a right handed shooter) and it's "cutting" to the left. If not then it's fairly easy fix to get to the part you need to modify/tune. Whether or not you should do it yourself or take it back to get it fixed or exchanged will depend on how you feel about it and if you're mechanically inclined. Note that 15 feet definitely isn't enough space to do any testing. Ideally you'd have at least 40 feet and I would personally wait til you get outdoors to fire at a milk carton or whatever they have at the field you're going to to see if your gun really is chopping BB's to the side as much as you say it is.
Now to do some diagnostics and possibly fix your accuracy problem (if you can't find someone experienced to help you with a fix and find on the field that it chops really far to the left) basically separate the upper portion of your gun from the lower portion (basically punch out the two body pins and pull it apart, keeping care to not mess up your charging handle, watch a youtube video on how to do it) and you'll see your hop up assembly and barrel on the upper portion. Pull that out; it'll look like this:
http://www.defconairsoft.co.uk/revie...y/DSC00383.JPG
Take it apart (again watch a guide, youtube is a great instructional tool if you can find a high quality video (and that doesn't mean some 12 year old saying "dis gun iz da best hurr durr)) and "reseat" the hop up bucking (as well as check for possible damage or if the top nub that puts pressure on the top of the BB to induce backspin is off centre).
Secondly; Hot water and twist with pliers or heat gun and twist with pliers.