Obviously Phil is being a bit more helpful than me there.
Trying to be a bit more positive: 1) you should expect some congestion and expect to run certainly the first 2-3 miles slower than you might like and 2) it's easy to burn more energy than you think side-stepping and getting frustrated. Even in front pens, you'll still get people walking 6-abreast in front of you. Try and be patient, and think of it as energy that you'll be able to make better use of later.
Phil is of course quite right that it's possible to change and it sounds like you should.