Spoiled Milk?

Look at my milk jug and its lid wasn't screwed on fully so I didn't think much of it. It's the day before the best before date and tried to not give into my safety nets and put it in my cereal. I put a scoop in my mouth and the milk tasted really off. I spit it out and smelled the milk jug and it smelled rotten. There were no chunks in the jug, but now I'm terrified that I could V*

I'm freaking out.

UPDATE: I didn't V* or anything. I knew I would be fine, but I panicked anyway. Thanks to all for the reassurance!