WELCOME TO the world of RVing...Be sure to see RV if you haven't.
The earliest we can camp here is usually April. We went for my birthday last year, but we usually can't make that call until we get closer. Too cold here.
I do know we will be camping by July for a family reunion, we already have our reservations, and the campground is nearly booked for that weekend already.
Be sure to check on your state park rates for camping, and reservation policies. They often have some of the best set-ups for campers, but you need to make reservations for any holiday weekends. Often those have to be made in the spring.
(Here you have to make them on the 1st Tuesday of April, starting at 8a.m., and it's first call first serve.)
Start Googling where you are going to go now

. It's always easier to cancell (sorry you had to), then not be able to go because someplace is completely booked.
HAVE FUN!