I am buying one of your Bitcoin shirts :) I hope it helps you tier up hehe. It looks like bitcoin is a good niche. there isn't a lot of shirts in there.

Oh I noticed that you have descriptions, But you aren't using your "keyword" slots. Make sure and put all your keywords in those slots. And maybe write out a sentence.
Like: Perfect for BITCOIN lovers.

Here I used my Merch INformer account to get you some insight on your Bitcoin Shirts...
Here are some keywords you may want to consider using.. THis is what people are searching on amazon.
I typed in "Bitcoin"

ethereum pure diamond logo white printed long lasting inks onto supersoft tshirt maximum comfort show support raise awareness shirt whether blockchain bitcoin developing apps spending ether perfect fan available mens womens youth kids sizes tee makes great gift unique lovers

I typed in "Bitcoin Shirt"
join movement raise awareness future currency one largest cryptocurrency virtual stheres bitcoin ethereum rest altcoins represent favorite world take financial control back step closer governing using blockchains smart contracts show support let known far wide

I hope this helps you out :)