Hi mrpb,
It sound like you're one of the lucky few who picks strumming up easily - good news! People vary a lot in how long they take to get comfortable with those, from straight away to a couple of months!
I'm currently working on the next few levels, and will have them up shortly, so that should give you more to practice, and maybe more of a challenge. If you want to continue practicing level 1-3 in the meanwhile, I'd suggesting trying to really lock in to the rhythm, playing each strum at exactly the right time. This can always be improved, and is worth practicing...
The idea with the lessons I'm posting is that you get comfortable enough with swinging your arm no matter what that you can pick up any rhythm you hear, first go, no having to rehearse or learn it. It sounds like it won't be too long until you're at that level, which will really open up your playing, and will make learning songs much easier...
James