Remembering Steps

I can see now why it is so important to practice the tango very regularly. I truly want to remember the steps and to master them, but I simply don't have enough time. Thus, when I come to class, it is the only time I am learning during the week. It is funny, because I will forget some steps from the previous weeks, and when I dig through my memory to get them down, I sometimes do steps we have learned, but the wrong ones. Also, just a side note, I am still confused whether I can do whatever steps I want during the Milonga, or if it is stricter than that.