I will just add the following to the excellent advice already:
The Heathrow Airport app is useful as it can give you step by step directions and has detailed maps, plus it is a reminder of your gate number.
If you have iOS an Apple iphone for example, here is a link
https://apps.apple.com/gb/app/lhr-lo...rt/id427951859
To get to the gates you need to get off the shuttle and go up the escalator or elevator/lift. The elevator is quicker.
Good luck - this can happen to anyone!
Step by step navigation
Here’s a map of B and C gates