Need help

Jesenia

I'm new a crocheting I'm about to have a baby any day now so I did him a cute simple blanket and wanted to do some mittens, beanie and booties to go with it. But the yarn that I have ( it was a gift) is red heart super saver 4 medium and it says it need 5.5 mm hook but the mittens tutorial says I need a 4mm hook which I got but can I use it anyways? Will the mitten come out bigger? This is the yarn she is using