Did you have success with 2nd trial from the same stylist)?

I would find a new person but I would maybe nicely say up front that you did not fully like how the style came out the last time and could she do as promise and style how she would the day of. If you are not still impressed I mean there is no logical way to do this without offending her but your day is important but I would look for another stylist. It is hard because it is great she wants to help you and I am sure she takes pride in her work but some people are not style experts. If it does not turn out as expected then do you feel comfortable telling her upfront that it is not looking how you expected and see how she reacts? Sadly I had a realization like you in that I am going to have to fork over the extra money to get hair and make up done. I do not want to but we deserve to look good on our day.

Your bridesmaid hair definitely looks better than your trial!

If there is doubt, you need to move on. I know you are worried about hurting someone's feelings but ultimately it's your wedding day and you need service you are confident in. And hair and makeup is an expense yes but 125 bucks is worth peace of mind I think.

Let the girl know you liked the trial but have decided to book a professional instead.

She's scheduled this Sunday, I'll tip her well even though she isn't charging extra for the hair. I feel like she should be able to do a better job since she did better on my hair as a bridesmaid but there's a specific look to the bridal hair I want.

I guess I don't know HOW I should tell her should I go with someone else. Do I tell her right then and there when I'm looking at my hair doubtfully (if it doesn't improve) or do I have my expression do the talking, tell her thank you, and then text/call her about the change? I feel like doing it on the spot would be super awkward.

Give her a chance this weekend.

Then, if you don't like it, go home and think about it and look at other options before you cancel her. I would do it later to avoid awkwardness.

Hmmmm maybe preface the style saying that you are particular about how you want your hair to look and you totally appreciate what she is doing for you but you would like it to look a certain wait and for her to put the full effort in this trial. If it does not look well then after than she should not be surprised if you go elsewhere but I would say that it would be best to tell her if you do use someone else so it won't be a complete shock to her.

https://youtu.be/C2pEBXj1VvY