Checkpoints in the text
Why does he hope it could be "anything"?
There might've been a one in a trillion chance that Alicia was going to deny him when he thought he could guess what was wrong, and say "I'll bet you can't". He doesn't want his life to be over yet, and don't really want her to be pregnant.
What is not quite right about what Alicia is saying?
Alicia says that as long as the baby is inside her body, it's hers, but after it's born, it's theirs. Sam doesn't see the logical explanation in this, because in this case, he doesn't get to choose for the baby because it's not his, and therefore he doesn't have any saying wherever he wants the baby or not.
How does Sam feel? Have you ever felt like this? When?
Sam feels anxious. He doesn't want to tell Alicia's parents, or his own for that matter, about the pregnancy. Personally, I've never been in a situation like this, so I don't think I've ever been so nervous to tell my parents anything that I make up lies to put it off.