1. Sell some items: choose to sell some low-quality items to make room for other more valuable items. By clicking the sell option, you can sell unnecessary items, get some gold coins, and leave a grid for new items.
2. Use props to increase the number of squares: In the Fat Goose Gym, there are some props to increase the number of squares. Check the in-game store or reward system, find these props, and expand the size of the board to accommodate more items.