I completely understand! Wally gets neutered the 31st, and I am worried too. But, I am sure you have an excellent Veterinary Surgeon and he will be perfectly fine! In 2 or 3 days everything will be back to normal!
Many, many dogs get neutered every day, and the recovery period is only (about) one day.
Everything Will Be Just Fine! Give your pup lots of love! Take a deep breath, and it will be over before you know it!
Tomorrow night he will be cuddling you!