When people let me review their portfolios (on career day or open days at my game design school) I explicitly ban them from commenting during the review… …because otherwise they will follow the impulse to downplay everything I see in an attempt at being humble.
"this is an old image…"
"I’m not happy with that one…"
"this is just a sketch…"
"I did this really quickly…"
"there is better stuff on later pages…"
It’s totally understandable to have those impulses. The quality of art is not empirical data and therefore impossible to measure. Good art, bad art, it all comes down to standards. And you don’t want to come off as naive or self-absorbed.
But just don’t do it. Don’t talk yourself down in front of others. In the best case you have someone supportive who now thinks “damn, this person needs to be prepped up all the time. Do I really want to work with somebody like that” or in worst case “now that you say it, yeah, this is kinda lame/rushed/unfinished/lazy, go away.”
You can only submit what you have. If that is not enough, then it’s not enough. Your attitude will not change that. But if it is enough, you can do serious harm by not being confident of who you are now.
This means appreciating what you are able to do right now and have a clear vision of what you want to learn, be confident that you will learn it in time.