It's probably settled:
Step one; stir it with a cocktail stick / toothpick. If it has gunk in the bottom stir till the gunk is broken up a bit.
Step two; shake it till your arm hurts, then shake it some more.
Revell paints tend to be very bad in my experience, but 'Flow all over your model' sounds like a brush control issue. Have less paint on your brush, and you'll find it won't flood so much, or at all.
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