I felt the exact same way, my daughter was 20 months when I brought my son home. Leading up to his due date I would break down and cry while cuddling her because I kept thinking “ Did I do enough for her in the time being?” We spent everyday all day together and now her whole world will be flipped with a new baby in the home but the first day she met him she put her head to his and showed me that she wanted to be gentle and nice with him. It’s totally fine to feel guilt and worrisome about a new baby but your also bringing happiness and more love to your family and it will show as soon as you have him. 
You got this mama.