I might suggest heading a little east for your first camping trip and come to Frederick (about 45-minutes to 1 hour from Bowie) and camp at Gambrill State Park off of Route 40, just outside the city limits. It is easy to get to and close enough to Frederick that if you forget anything Wal-Mart, Target and K-Mart are very close.
In addition, there is a great locally owned outdoor store “The Trail House” in downtown Frederick, which has most of what you need and a very knowledgeable and friendly staff who are more then willing to take the time and talk to first-time/novice campers on their needs.
Gambrill has some excellent well-marked trails ranging from very easy to moderate and some beautiful vistas. The campground allows you to keep your car at the site and offers pads for you to set up your tent.
Depending on when you might be able to camp at Gambrill, I might be able to stop by and say hello or join you on a hike.
Pete