How do I mathematically convert the figure for my Electrum wallet balance into USD?

1. What’s the best way to use BTC to shop at Amazon and other online retailers?

2. One source says the answer is to purchase gift cards at sites like Bitrefill.

3. I tried buying an Amazon gift card on Bitrefill but hit a glitch: the software showed a fee 100 times the purchase price.

I hope someone can clarify these issues!

I joined Coinbase, made my first purchase of BTC, then tried to transfer some of it to my Electrum wallet. The BTC was sent but failed to appear in my wallet. According to an answer on this forum, I should have used the Receiving address, whereas I used an address from the “Addresses” section of the wallet. Presumably this was the cause of the problem, and if so, my question now is whether there’s any way to still get the BTC into my wallet, or has it vanished forever into the cyber-void?