How can I check if my seed matches a BTC address?
In HD wallets it rarely happen that a gap of more than 20 is being used. It relates to bip32 standard in most cases. And it may happen in only few cases:
-if the receiver is a payment processor that puts out hundreds of invoices and only few are being paid.
It doesn't sound like your case though. I would suggest using IanColeman website, please remember to use it in offline mode and be very careful about it anyway. I wouldn't use it with a bigger amount of funds personally.