Don't worry, 4 weeks is plenty of time to wear in. I ran about 20 miles before race day in my last marathon shoes and had no problems.
However, as someone who used to wear Pegasus a lot, Nike seem to change the fit and feel of them every year. They've gone downhill since 25 in my opinion and I find them almost unwearable now.
Although I have been transitioning to more minimal shoes over that time which might have something to do with it.