Maz,
Don't worry mate! Remember all that advice you gave me when I was getting frustrated with my landings.
Don't forget all that human factors stuff either. Feeding in a load of new tasks it sounds like you're trying to do everything consciously. You can now fly the aircraft without doing this (you had the airspeed correct), so that's one thing out of the way. It also sounds like you were shocked by your altitude deviations (see below) and the difficulty of map reading whilst trying to fly in marginal weather.
I haven't started nav yet, so I have to profess considerable ignorance, but Sheepy's suggestion of using Flight Sim might be worth a try. I recon some areas of the photographic scenary are better than others, so I'm not sure how much help that would be. However, my instructor often talks about the need for practice to keep up 'scan rate' which sounds like it might have been an issue for you (with the altitude problems). FS might help you practice juggling the chart, simulated radio calls (without anyone to tell you off!), rough location (and you can double check using the GPS function!) and scanning airspeed, altitude etc all at the same time.
Don't worry - perseverance will pay off - and I'm sure you'll have a better lesson next time. Mine got cancelled yesterday - occlusion arrived over the airfield at just about the same time as I did
Paul