When one says "don't read too much in it", does it mean not to worry unnecessary or not to exaggerate things or it has some other/more meaning?
You would normally say 'Don't read too much into it'; "reading too much into something" is over-interpreting, seeing an unspoken intention behind the words:
'We used to live together, and now she's asked me out to dinner without her husband. What do you think are my chances of re-kindling the old flame?'
'Don't read too much into it. Maybe she's planning a birthday surprise for him.'
If there's a document involved, there's a similar expression: 'reading between the lines'.