Just to give you some alternatives where you don't need a scooter, if you're interested. There are hotels right off many metro stations. The Crystal Gateway Marriott in Virginia is right off the Crystal City metro (on the Yellow Line) -- you don't even have to go above ground to get there. Once you're on the subway train, it's about a 10-15 minute ride to Mt Vernon metro where the WEWCC is. There's another Marriott there at Crystal City metro, but it's farther to get to (you don't have to go above ground for that Marriott too). To get to the Crystal Gateway Marriott, when leaving the Crystal City metro, you'll be going up some escalators and will see doors on the left and right, and you'll see more escalators ahead of you. Take the doors to the right. There's a small mall with a convenience store, a Rite Aid store and restaurants. Near the Rite Aid store you'll see a small tunnel which goes to the Crystal City Marriott.
To get to the other Marriott, you'll take the doors to the left (instead of the right in the instructions, above), and you'll be walking down many long, long hallways to get there. (Not really great, late at night, IMHO.)
There's also some hotels close by the Bethesda metro (on the Red Line, so you'd have to transfer to the Yellow Line to get to the Mt Vernon metro for the WEWCC). The Hyatt's right above the Bethesda metro. And about 2 blocks away are the Marriot Residence Inn and Hilton Garden Inn.
I've been to all these hotels, and they're all great to stay at. The Crystal Gateway Marriott would probably be the most handy since it's right on the Yellow Line for the WEWCC, and has a Rite Aid (for hotel room supplies) and restaurants and other stores right next to it. (The last time I was there, about a year ago, just some of the stores were open on Sundays. The Rite Aid store was open on Sundays).
Anyway, you've probably got your hotel all set, but thought to post this info, just in case.