Aww don’t feel bad about the nail trim. Everyone has done this at one time or another. I’ll bet when you cut the nail you probably clipped a small area of the quick and that made him yelp.
I would definitely ignore him and let him get over this behavior on his own. If you try to console him or feed treats you are telling him it’s okay to act this way. If possible hook him up with a harness or collar and take him for a long walk. I guarantee he will forget about the nail trim. Continue the rest of the day as if nothing unusual happened.
Since you had a minor mishap, he might be a little difficult to trim next time. So when attempting to do it again, be very patient and do not let him pull away from you. You MUST complete the job even if it’s only one foot (or nail) per day.
I usually have my dog’s nails trimmed by a Tech at the vets. I understand Petsmart does nail trimming too. If this is your first time trimming I’m sure either one (the Tech or Petsmart) will gladly let you watch so you know exactly how to trim without problems. Another thought, I'm sure the ASPCA would do the nail trims too.
Here's to a long happy life for the two of you.
I wish you the best!!
p.s. My dog usually gets her nails done every 3 weeks. So I would do it more often than you have been, he will eventually get use to it.