I know and understand that 11 day seems like so far awa, but I would NEVER go behind my hubby's back and schedule a scan for the pure intention of finding out what the gender is.
I had an u/s for emergency reasons before my gender scan. I happened to find out. Hubby was elated but disappointed that he couldn't be there with me. He has ALWAYS been there with me for all of my scans. The fact that it was an emergency scan made it impossible for him to be there at that time though.
This is news that you should be sharing together and not hiding from each other. What happens if it isn't the gender you want? He's going to wonder what is up and why you are down. If it is the gender youare hoping for...are you really going to be able to keep it from him? Or will you spoil the big surprise?
Honestly, I would wait. It would only be an extra 8 days and you would be savi9ng that money that could be used to go toward something for the baby. Remember that you and your hubby are going through this all together. As a team, he ought to be at least made aware if you do go through with the scan on Monday.