If you'd like your project to turn out as strong, solid, and lasting as if a professional woodworker built it, do what they do...use your tri-square to check for squareness after each cross cut. Edges on boards that will be edge-joined must be absolutely square, so carefully check all sides. If a cut is not exactly square, use a block plane to trim. It takes a little extra time, but the improved results will be well worth it.
There are no easy ways to improve your credit score, but you can work to keep it acceptable by maintaining a good credit history. This means paying your bills on time and not overextending yourself by buying more than you can afford.