Visitor to Spousal Visa

Hi there! I'm a new member and in need of a little advice.

I'm an American, and my husband is a UK citizen. Right now I'm living in England on a 6 month visitor visa while he works to fulfill the financial requirement for us to apply for a spousal visa. There are only a couple of months left on my visa so I'm preparing materials for our spousal application packet so I'm ready for when I return to the US to file.
I was under the impression that I would be able to start working on the online application while in the UK, then when I got into the US I could submit it and get the ball rolling as soon as possible. However, now I'm wondering if starting the application online will be a breach of my current visa, which would be disastrous! I don't want to do anything that would jeopardize our future visa prospects! I know from completing the visitor visa application that the date you start the application is logged online, regardless of when you actually submit and print it.

Would trying to start it now be a huge mistake?