I unclip when my foot is up, rather than down, because that's what I was used to doing with toe clips. It works fine with my spds, even though it takes a tiny bit more effort. If you're more comfortable doing it that way, I don't see that there's any problem.

Can you borrow a trainer and practice a lot with your bike secure? Are your pedals at their very loosest?

Keep trying--it's so worth it, once it becomes second nature.