Dogs tolerate simple aspirin products (offered only on occasion; they may cause stomach upset or ulcers if given too frequently, plus they are a blood thinner, so it may completely inappropriate in some animals).
An 8 lb dog would generally be given ½ of a baby aspirin (40 mg) or less.
A 64 lb dog should be able to have one (320 mg) adult aspirin.
Never more than one a day and never more than 3 days without blood tests/monitoring by your vet
That said, it may really be worth the vet visit for an X-ray. A break or fracture may bleed, infect or complicate internally and by the time you become really aware of it, it's too late (or highly complicated and expensive to treat). A bone fragment may break off and enter the bloodstream causing a blockage/stroke and an apparently 'fine' dog is found lifeless without warning.
Keep the dog on low activity until you can have him seen.
You might also want to try a rice sock (heat). Take any clean sock, fill 3/4 with plain, uncooked rice, knot the end and microwave it 1 to 1 1/2 minutes. Shake it out to distribute the heat and be sure it's not too hot - it stays warm for quite a while and isn't as dangerous as a heating pad might be.
Good luck - I hope it's all good!