Based on pictures he is just fine. They like laying down like that. Mine is even eating laying like this. Take a short video from behind of him walking - would be visible a bit better I think.
Also, they still have puppy legs at this age and will be awkward looking and clumsy.
If you are concerned though, just talk to the vet. They will feel the legs, stretch, see how he reacts (if there is pain and whatnot). If there is a concern, maybe they'll suggest an x-ray. But from what I've read, until 1.5-2 years old bones still grow and unless there is a serious concern, not do it until that age.
Please be gentle on jumps. Don't let him jump from higher than his height. Joints are fragile still at this age and heavy impact may cause more harm than good. Just walk him and run gently (a gentle stroll).