No.
You may use whatever software you are comfortable with. Just be aware, if you are uploading a complete design, make sure that it is 1050 pixels (minimum) on the longest side. If you are unsure how to do this, don’t worry—send us what you have and our professional designers can recreate it in high resolution. (If you are using a photo background, make sure you send us the full, high-resolution photo along with your design.)