I agree. Eat the whole thing or don't do it at all.
Don't go doing part of it is just a waste. If you don't do enough to begin with you won't get off, and you can't just "add onto" the dose later expecting to get "higher" or "last longer". Once it's in your system you're done with shrooms for at least a week, so just remember do it up or not all.
I've never heard of or witnessed anyone taking too many shrooms.. I have however on numerous occasions not gotten off from taking too little.