your first and biggest mistake:
you are trading XRP with ETH but you are looking at prices in USD! that doesn't even make sense. you should check the price in ETH not in USD. if it is different then move ahead.
I assume you are using coinmarketcap.com to see these prices because I can not think of any other way you could see XRP/ETH price in USD. that is a big mistake because they report the last price not current price and it is update with 5 minute delay.
On Binance, you can see the USD equivalent right next to its last trade price. So even though looking at XRP/ETH market...the USD is also right there.
The whole arbitrage thing is seeming like the biggest challenge as i educate myself. Im so used to just buying XYZ in USD and it either goes up, or down. Not so in this world...its very daunting. BTC/USD BTC/ETH BTC/BNB etc etc ...there's tons of ways to directly and indirectly play these coins (at least the major ones)...its such a difference than other tradable instruments.