I second Iceblossom's advice to 'fess up - your girlfriend probably will not be thrilled with what happened - but it sounds like your actions were not malicious - so -
Maybe between the two of you, a fix or solution (or resolution) can be found.
For future reference - generally speaking - protein based stains (urine, blood, feces, vomit) come out better with cold to barely warm water - hot water tends to set those stains. After the loose stuff has been flushed away - or washed down the drain - then apply some detergent/soap to the stain - wait a few minutes - and rubbing the fabric together (i am long past the ewwwwww stage - but there is that to contend with - get out the water proof gloves if you are squeamish) helps remove - or at least lighten - some stains.
And the sooner the better.
Do that before washing the whole item.
This is an interesting article:
https://www.agingcare.com/articles/r...ics-151216.htm
There are specialty products for set in stains - but for relatively fresh stains - the cold water, detergent/scrubbing, washing usually gets most of them out.