How much lower from the CU and what is your score? What kind of loan?

Remember you never HAVE a mortgage until the last paper is signed and the keys are handed to you.

100% at 8.8% rate… like it’s been said, either your credit is in the toilet, or you are getting ripped big time.
If your credit is not so great, I’d be careful as 100% loans for those with less than perfect credit are not as plentiful these days (in fact even if you are getting a Freddie or Fannie Mae loan which both offer this, you very likely will not be able to get mortgage insurance as the MI companies have been cutting off low scores and high loan to value loans, ask your mortgage person for more information on the planned loan, ask a lot of questions, and then ask a lot more).
If you have better credit, shop around you are getting skunked. The credit union is not the place to go if you want 100% financing, but could be a great place if you have some money to put down (they often limit loans to 95% loan to value).
Some questions you need to look at, how long you plan to be in the house, what you can do with the money you might have to put down by leaving it elsewhere (not just the interest return on it, but how having some money in the bank will make you feel, it can be a big thing to keep you from freaking out about that big new mortgage you just got.)