If you are a skinny bitch then just keep going, you are too skinny to worry about proportion. Come back after 2 years of solid effort.
If you are not a skinny bitch, it is possible you may have some sort of structural imbalance, however I doubt it. Why don't you post a pic of your disproportionate pecs.
Or you could describe the size of them to us.
Oh yeah and finally some valuable advice. Dumbbells exist too.