Youve got nothing to apologize for, you just stumbled into a bee hive... Really just boils down to authority and ego, but none of it is your fault
Good choice on the G-Flex, like i said its hands-down the best ive used, and shockingly theres next to no price premium on it. As far as cleanup of the squeeze-out goes, theres actually several methods you can use. The most obvious one is wiping it off with a solvent while its wet. Denatured alcohol and acetone both work well for this, but its a messy process. Ive hear tales that baby wipes do the job well, but i have more acetone on-hand than small children, so i cant vouch for that. You can also chip/sand the excess off after its cured, works but not my favorite method.
What i like doing, when the situation allows, is a bit of a compromise between the aforementioned methods, and will work for you if both the pieces are already pre-finished. First, dry assemble the joing, get everything looking how it will once the glueup is done, then wax the entire area. Dont get any wax where you want glue, of course, but get it everywhere that you dont want glue to end up. Once thats done, glue up as you would otherwise, but instead of walking away straight after, wait until the epoxy has gelled, bout an hour or so with the G-Flex. Then, come back and just pop off the squeeze out. No mess, no fuss, and the wax just buffs off afterwards. That said though, dont do this on unfinished pieces, the wax will prevent finishes from adhering!