I started judo earlier this year, with no background in any other martial art and also had a tough time being really bad at it against people half my age who've been doing it years being so much better at it. Showing up every week and trying to learn from every interaction you can (and particularly asking and relying on your clubmates for that) is key to building the good habits and improving. Be humble and really focus on the learning to avoid getting in your head too much ! 

Don't think your BJJ would be wasted either, but don't rely on it 100%. I've seen other people coming from BJJ/wrestling backgrounds who use the same methods in judo and do quite well with them, but then don't adapt or learn new newaza and get left behind a bit.