It's only 3 weeks. In the greater scheme of things, it's nothing and you have your visa and a future together.
If you are so desperate to see her, you can arrive as a visitor, and then leave UK for France, for example, and return on or after 1st Nov to activate your spouse visa. Immigration officer will want to see evidence of your short trip to France such as flight or Eurostar booking (you can make it a short holiday together, or even a day trip). Or just save all that money for later and just get ready for your move to UK.