Select the composition before choosing pixels
An Illustrator document can hold several artboards and hidden alternatives. Choose the intended board and decide the display dimensions before export. A vector source can scale widely, but the PNG has a fixed number of pixels once it is created.
If the asset will appear at several responsive sizes, prepare suitable versions from the AI source instead of enlarging a small PNG. Name each file with its placement or dimensions. Keep a record of the board and revision that produced the image.