Racehorses aren't usually skinny, they are fit :]
Looks like you were having a good time. You only just started jumping him, right? That's a pretty decent and mean jump for a begginner! If I were you I would do some grid work and nice, friendly little jumps until he builds his confidence and learns where to put his feet. A ground pole is a MUST for horses learning to jump, it helps them to judge the correct distance.