Log Cabin seems easy because it'a all straight sewing; however, the thing to remember in all quilting is accuracy - both in cutting and sewing consistent quarter-inch seams. Try to let the fabric feed through the machine without tugging on it because that could skew it too. In the end, keep at it and follow the advice given ... either cut them down to the smallest block or add another border and cut it down so they're all the same size.