Carolyn,
Welcome to the board and your new addiction to quilting. None of us is perfect so 'mistakes' are very acceptable. Like we all say, no 'quilt police' will come knocking on your door.
I, personally, have found my basic rulers to be the best - they are the ones I always turn to....my 12x12 and 6x24. I also have a couple of other specialty rulers but rarely reach for them.
Keep going....your first will be the one that you measure your improvement over the next and the next one.
Have fun and happy quilting!
Debbie