Sounds like a regurge. You'd have to share a lot more details about what you ARE doing before we can help you figure out what you're doing wrong.

What kind of cage are you using?
What temperatures are you keeping in the cage?
How are you maintaining those temps?
How old is the snake?
How long have you had it?
Has it eaten successfully for you before?
Do you handle it much?
Did you handle it much since the Thursday feeding?
Does the snake have a quiet, secure place to hide while it digests its meal?

...and any other details you think might be pertinent to figuring out what went wrong.