According to the balloon material and environmental conditions, the balloon arch may shrink after two days. Generally speaking, balloons are made of rubber or plastic, and they will gradually lose gas, causing them to become slack or deflate. In addition, environmental factors such as temperature, air pressure and humidity will also affect the holding time and shape of balloons.

If the balloon arch is made of ordinary balloons, it is likely to lose some expansion and change its shape after two days. However, if professional balloon materials and techniques are used, the arch may remain inflated for a long time.

Therefore, after two days, the balloon bow may be deformed or partially deflated. If you want to keep the shape and inflated state of the balloon, you can consider inflating some extra gas, or putting the arch in a stable and dry environment.

Please note that the above answers are based on common sense and experience, and different kinds and methods of making balloons may have different characteristics and holding time. The specific situation needs specific analysis.