question on contrary motion scales

Hello,
I started playing piano two years ago and I've played scales for a few months now. First I play them reading the sheets, then I try to play looking at the keyboard and finally I play without looking at the keyboard. So far (up to 3 sharps and 3 flats) I have no difficulties for scales in straight motion. I can play contrary motion looking at the keyboard (not very easily anyway!) , but no way I can play them by memory -e.g. without looking at the keyboard. Do you have any suggestion for that? Thanks.

I think just practicing them, and taking your time for accuracy and gradually working up. Just a few weeks ago I was not able to do any scale in contrary motion, even when looking at the keyboard (well, except maybe C major and A minor). But just by practicing everyday, and slowly working my way up in difficulty I am now able to do probably about 1/3 of the major scales in contrary motion fairly easily without looking at the keys, and am getting better everyday.

The way I do it is first start off looking at the keys. Go slowly and make sure I'm hitting every note. Once I have that down I start gradually looking away, maybe for note or 2, in parts I know I can do. More and more I keep looking away for a little bit longer, little bit longer...until I finally have the movement locked in my brain and hands...and once that movement is locked in and my brains and hands know how it should feel and sound I don't have much difficulty.

I don't know if there is a certain, more preferred way for learning them, but this is how I do it and it seems to work.

Have you not learned the patterns for remembering your scales?

Major Scales are Tone, Tone, Semi Tone, Tone, Tone, Tone, Semi Tone
Minor Scales are Tone, Semi Tone, Tone, Tone, Semi Tone, Tone, Tone

I know the patterns , but when I play scales I use note names, trying to remember the accidental signs. For example: D major => C#,F# . For contrary motion scales I look at my left hand on the keyboard , while I mentally sing the scale for the right
hand. When I see/sing a C or a F I know I must hit a back key: is this a wrong approach?
Anyway thank you to ZoologyGirl and Alistair123 : I will apply your suggestions.