I'm chiming in so the OP isn't sitting their chewing fingers to the bone thinking the BP is screwed up for life.
I fully agree with Slim's points on gerbils and am adding a few points of my own:
1. Gerbils and Hamsters are considered "fatty" compared to rats and mice and are frowned upon with feeding to a snake for reasons previously stated.
2. It may not be the end of the world, it is possible if the snake is hooked on gerbils to bring it back via scenting a rat or mouse with a gerbil.
3. Story- My sister's BP which is now in my possesion ate gerbils for the first 2 years of its life. She said they tried mice and rats and the snake wouldn't even look at them. I take possession of the snake and waited 2 weeks to feed the snake. First thing I offered was a small-medium sized rat which it wrapped right up but let go after 5-10 seconds either cause I spooked the snake or because the rat was too big/strong at the time. I proceeded to feed it mice for the next month, each time it took at least 3 mice without a problem. Then switched to small rats. The snake did not have an issue with switching in my case. Every snake and situation is different, I probably am lucky to have a BP which switched without a hitch.
4. Patience. You must learn patience. These snakes can and will put you on edge and rattle your nerves. One of my BPs stops eating in October and will probably start eating again next month. He(assuming it's male) is following the same pattern as 2 of my colubrids. It was very frustrating when he did this last year cause I didn't expect it. If he doesn't start to eat, then I know a change will need to be made.
5. As the snake has now eaten for you, I'd recommend the next feeding be a small rat or an ASF. If anyone has a better recommendation, Pleas override this suggestion.