Katie,

I think that you would be better off starting again. In my experience, when
the buffer boils off you are at risk of getting false negatives. In fact,
you can often see the level of buffer that boiled off because above that
level the positive control is negative and below it is still positive. If
you notice that the buffer has boiled off you can repeat the antigen
retrieval procedure immediately and this sometimes works. The only way that
I have discovered to prevent this from happening is to always use new coplin
jars and make sure that the lids aren't on too tight. I hope that this
helps. Tom