Please advise: Valid From date

Greetings everyone.
I received my shiny UK YMS Tier 5 visa today. On it however I noticed is the "Valid From" date of 1 July, 2011. The issue with this is that I set my "ESTIMATED" travel date in July just in case. No one told me at Worldbridge that meant this is the date I was going to have to enter on, or afterward. Truth be told I want to leave in 3 weeks!

Should I send my passport back with a letter asking for a correction to the British High Commission in Ottawa (I am Canadian)?

Will they fix it? I have a job lined up for when I get there and I won't be able to start until July 1st, and probably will be denied entry PERIOD! Thoughts?

There is no clear yes or no answer. 

In your particular situation the BHC can do whatever it wants. 

If you are going to try for an amendment to your entry clearance, I would suggest using a priority service if there's one available, but it's only free advice and not a requirement.