Given head to a huge dick...

So most of the guys i have been have all said i give amazing head.. they were average size. Well now I’ve been dating someone who has a huge dick and Its making me feel so self conscious because i SUCK at giving him head and he loves to get it. It’s so thick that it’s hard not to scratch him with my teeth and it’s so long that it’s hard to even get it all in my mouth without gagging.. plus he takes forever to finish so i always end up just giving up and we have sex instead. But i know he really wants me to finish him from head. I need tips pleaseee! Anything at this point will be helpful.