The forward bid-ask spread must be enlarged, so if the remittance is a large number/decimal number, subtract the remittance from the spot exchange rate and add it in turn.

This topic is not very clear. Should idle dollars be invested in pounds? If so,

If you buy at the spot exchange rate, after three months, the pound will depreciate and you will lose money:

3500000 * ( 1- 1.5 12 1/ 1.5380) = $58940.

Buying pounds at the spot exchange rate and selling three-month forward pounds at the same time will lead to losses:

3500000 * ( 1- 1.5 160/ 1.5380) = $50065.

Whether arbitrage can be profitable depends entirely on the change of spot exchange rate in the market, and arbitrage can lock in the future exchange rate through forward trading.