Yes, check your gauge and then if something's still off, make sure you're doing the stitches correctly based on where the pattern originated (UK or US).
Here's a link to a conversion chart just in case you need to refer to it:
http://www.yarnfwd.com/main/crochet.html
Oh, and congrats on completing your first amigurumi, which I can't pronounce and can barely spell, let alone have the patience to crochet and sew those crazy things together!!