Try to practice crawl, still plenty of time.
I had the same problem. In the beginning I was not able to do 50m crawl. Then I practiced with a pool buoy and focused on long stroke. I find swimming with the pool buoy is very similar to swimming with a wet suit. I hardly use my legs, someone told me I should just keep them relaxed, they will be required later.
Good news is you HAVE to use a wet suit in London tri (whatever the temperature will be like on that day). In other events wetsuits are not allowed if the water is too warm. In addition there is no current or tide in the dock, it's dead easy, just swimming along the rope. No sea lions, sharks, other big fish, very very easy and safe.
Then I read a book called Total Immersion by Terry Laughlin, this gave me a bit of idea about technique. There are master classes too.
Yes, I agree practice orientation. The water in the dock is quite dirty (very very deep green) and you usually can't see anything. Maybe look around every 50 strokes (but don't stop), there are big yellow ballons, this will help you.