1) Always ship your weed inside an actual package of some sort. You could buy a $15 pair of Walmart shoes, for example, and stuff up to around 3 ounces in each shoe. Then overnight the package.
2) Whatever hard drive you used to query the shipping website, put it up somewhere away from your location for a while. Simply buy a new hard drive and pop it in. Even if there is an IP match, it won't matter. There will be no traceable evidence on the new drive.
3) If the police do attempt to question you, do not answer any questions. Period. An IP hit is one thing, proving it was you behind it is another.
4) Don't get your package flagged again. That was lame of you.