We found a pergola design that we loved and copied the design but now that it's (mostly) up we are questioning its stability and safety. The 2x6 beams are notched 3" to fit together, which I have read makes them equivalent to 2x3's. We love this design and want to make it sturdy and safe. We plan to put diagonal supports from the posts to beams, but wanted to seek advice before we proceed. The louver boards (see the second picture, they will be built in each of the 8 openings) have added a load. We want to make this stable.