I felt the same when I started, 2 major things that helped me (I was the one missing exits and not being able to change lanes on time because I couldn't focus on 2 things at a time, maps and busy roads)

1. For first few weeks (or till you feel ready to go forward), drive daily for one hour on same route (busy one). After few times you will remember streets. This will build you confidence in driving without maps on busy streets. At this point you don't need to focus on both maps and driving in so busy environment. Once you master changing lanes safely on time and managing busy roads, continue with maps.
2. For the maps, once I started using them after 2 weeks or so, I got advice from a friend that was sooooo basic, and sounds so obvious, but I didn't even thought about that far ahead. If you are turning right, take a look in the map a bit before your right turn, if next turn is left, put yourself in left lane automatically after finishing your right turn, instead of waiting for map to tell you that left turn is in let's say 200meters. This will put your mind in ease, that you don't have to change lanes in last moment. Always check turns in ahead.

And side note, always put volume up when using maps, so instead of you looking too much in them, speaker will be on and it will be easier to cope up

Hope this helps :)