Formaldehyde breaks down quickly in sunlight or when bacteria get to work.
Humans metabolize formaldehyde quickly into formic acid, so repeated small doses do not accumulate in the body. It takes VERY little (1oz of 37% formaldehyde solution) to kill an adult human or cause serious upper GI tract damage, but that's a very concentrated solution.
Prime is probably less than 5% total volume.
That's not to say you should chug it or anything, but you have very little to worry about, as the formaldehyde in prime will break down very, very quickly once it's out of the bottle.
Many beauty products and creams/lotions contain formaldehyde. Everyone thinks about specimens floating in jars of formaldehyde, but it has a wide number of everyday uses.