How to Cut Smoothly?

So far, so good. I cut two basic muzzle pieces out of 1-inch foam and glued them together.

Fine shaping is a problem right now, because almost every time I snip off a piece of foam, I end up taking off more than what I intended, or it just is jagged and uneven.

Here are some photos of the head base and muzzle:

1. Balaclava head base, eye mock-ups added
Image may be NSFW.
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2. Muzzle side
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3. Muzzle front
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4. Muzzle back
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5. Concept art of finished head
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Obviously, I need to build up the sides, even them out, round the entire muzzle, and hollow it out. I just am hesitant to do so, because of the problems stated above.

Any tips or advice would be greatly appreciated.