Hi Anida, I helped my carpenter put tounge and groove flooring on my porch and the most important thing I learned was to measure the distance from each end of the last board installed to the end of were the last board will be. We did that after every five or six boards. That distance should remain close to being the same as you put the boards up. We made three or four minor adjustments if we were off. If not you will end up with an angled board at the end. I think your right to be concerned about the first board. You should measure the starting distance as well and make small adjustments.