I got pregnant with baby # 2 when my daughter was 14 months old. I felt horrible and guilty. She was the light of my life and there was no way I could love another person as much as I loved her. I was mad at myself for feeling guilty, and sad for my daughter that she would have to share any part of me.
When I got pregnant with # 3, the oldest had just turned 3 and my baby then was 14 months. I felt bad because I knew there was no way I could love yet ANOTHER person as much as I loved my first two, and I knew we would not have more than 3 kids, so I was making my poor baby a middle child.
Fast forward almost 5 years later. Now my baby is 4 (5 in March), my # 2 is 6, and my first is 8. There is more than enough love, attention, caring, play time, etc to go around for the three of them. And they wouldn't be who they are without their siblings being close.
Granted, yours will be closer, but that's a good thing. It will be HARD when they are little, but as they grow you will LOVE it.
My BIL and SIL were born in the same calendar year...he was born in January and she was born in December. My husband is 6 years older than both of them. The bond the younger two have is so strong...and my husband isn't as close to either of them.
Trust me, I think what you are feeling is normal and you'd feel it whether you got pregant now or in 5 years. Everything will be fine. Your daughter will be no less loved and the new baby will get just as much as she does.
Honestly, with each baby, it was like my heart doubled in size. I have enough love for each new one as I did before - even though my heart feels like it is ready to burst.
Congratulation on the new baby!!