Print on Flashforge Creator Pro is rough in spots

[verersatz]

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I'm using a Flashforge Creator Pro and PLA filament to create the object found here: http://www.thingiverse.com/thing:825780. I've been using both supports and a raft. You can see from the pictures that the top prints really well but the bottom turns out rough. I'm fairly new to 3D printing, so I'm not sure which things to alter to prevent this. Does anyone have any suggestions for what might be causing this?

Edit: if it helps to know, I am printing with 10% infill.