Blowjob, teeth, small mouth

Hi,

I really want to give my bf a blowjob (it will be my first), however he is quite girthy and I have a tiny mouth. I don’t think I will be able to fit my mouth round the tip of his dick, let alone have the shaft in my mouth. I don’t want to scratch him with my teeth. Any tips, how can I practice in advance?

Thank youuuuu