IMO…I don’t think there’s a solution for that unless you re-drill elsewhere but that’s why you measure plenty of times prior to drilling chief. I ended up doing my 50g lowboy fir the first time and my ocd made me check it all before drilling. Came out just under the inner lip of the tank and cleared the back with no issue.
Just silicone the holes with glass or plexi and redo again in another area is your only option. Or drill elsewhere on the tank and keep the resealed area to the back so you done see it.
Good luck