I don’t see how you can be subject to US law, since you are not selling within any US territory. I sell to USA - and worldwide - and have always given my non-UK/non-EU customers the same T&C & rights as I give to local customers.
Except: I make it clear that buyers outside the UK are responsible for any local charges - for example, Customs, Import taxes, local delivery charges. You can not be expected to know about these - it is up to a buyer to research such charges if they are concerned about them (in UK, items coming from abroad over a certain value - I think £15 - may incur a VAT charge via Customs & Excise and the PO charge for handling this on their behalf, so you would pay 20% of the item’s value, plus an £8 charge to the PO. US Customs may impose similar charges - or there may be something in individual states - but you can’t know this).
If you use the Post Office for your mailing, then they will know about local delivery charges, but I’m not sure about other companies (eg. I’ve heard of UPS levying a charge for a customer in US to pick up a failed delivery from their depot). So make it clear to all buyers - in your T&C section - that local charges are their responsibility.
Be sure to complete a Customs form correctly and attach it to your parcel; also check that your item isn’t on the Prohibited list - see the Post Office website for information about mailing items abroad. If you were to send an item that is not allowed, it would probably be seized by US Customs and confiscated. If it was classed as dangerous, you’d probably hear about it, but otherwise it’s likely it would just disappear. It’s up to you to make sure your items are ok.
Other than that, I suggest making it clear who would be responsible for the return postage, should the buyer decide to send it back and cancel their order.