I don't think having one child is a bad thing at all!
I have 2 older siblings but there is a very large age gap and I grew up virtually as an only child. My brother and sister grew up with my Father and I was with mum. So, they were never around and I saw them more as an aunt and uncle than siblings.
Anyway, I enjoyed being an "only" child BUT, there were a few things my Mum did that made it hard for me.
1) My friendships weren't encouraged. She wanted me to be home with her and wrap me up in cotton wool.
2) A lot of pressure was put on me to excel at everything.
It's often harder to parent one child than it is 2 or more. You're their ONLY immediate influence and, you need to be able to let them become independent and find outside influences more readily. AND, it can be hard for parents of only children not to spoil them too much.
If you can do that; you're child will have an amazing childhood:) There's nothing to feel guilty about and you aren't depriving your child of anything:)