I have electrum 2.7.18 installed on my rasp pi
That's the issue. This version of Electrum has synchronization issues and a important vulnerability (already corrected in new versions). You will need to upgrade it to the latest version.
Am nervous that if I uninstall the current electrum and update will the BTC still finds it s way there as long as I have the address it was sent to?
Do you have your wallet seed stored anywhere? If anything happens, you can just open Electrum and use the word seed to restore your wallet again.
If you forgot to write it down or just ignored the warning when setting up your wallet, you can see it again by going to Wallet -> Seed; Remember to always double-check the words to see if everything is correct.