Yes, it is certainly possible to overdo it. When decorating your tank try to strike a balance between choosing items that look good to you, and those that meet the needs of your fish.
Your betta needs room to swim around, and he needs clear access to the water surface. Consider including plants, live or artificial, as bettas sometimes will rest on their leaves. Provide a cave or decoration for shelter in case your betta decides he needs a secure place to hide.
Remember that every decoration takes away some tank space. If you include too many, your betta may feel stressed and crowded, just as if he were in a tank that was too small. A tank that’s overcrowded with decorations will also be harder to clean and allow more places for waste to get trapped.