Everything needs to flow downhill from the outlet of the p-trap. Plus, you are only allowed 135-degrees (I think) before it hits the drain on the trap arm. While it will take more room underneath, I think you should have run it diagonally with a 45. The plumbing inspector would probably flag this and make you redo it. The back slope will not allow hair and other crud to wash down the drain, and you'll be cleaning out a full trap periodically as well.