What happens at trial?

I have not yet been to trial because it keeps getting postponed : (I want things to get moving because I've been trying to divorce for 2 years)... But I would look for some other advice if you don't like your current attorney and especially if you don't think she's doing an adequate job. If you find a new attorney, most likely they can file a motion to delay the trial so that you can prepare. Each state is different so you'll have to research a bit more... Also, if you find an attorney and can't foot the bill right now, is it possible for you to put it on credit cards or take out a loan? I hate to give the advise of going into debt, but sometimes you have to do this in the short term. If X is taking you for a ride and shouldn't be doing this (and you have a good attorney), you might be able to recover some of the expenses.
Do you have documentation that X did not see DS? What's been your agreement in the past few months? Are you afraid that he has some 'dirt' on you or negative 'character' witnesses? It's all scary stuff. Does your state have court appointed custody evaluators? You don't say too much negative stuff about X, but if he's trying to make you look bad, you're going to have to get your own experts to fight him...
And yes, you can be put on the stand as a witness.
Hope I'm not rambling too much, I'm really burnt tonight.

What state (or country if not US) are you in?

I am a lawyer (not a family law attorney), and I have been through my own divorce trial. I can say for sure that, almost anywhere in the US, if you are not already prepared for trial, it will be extremely hard to be prepared on Friday. There are discovery deadlines -- you are supposed to have provided the opposing party all exhibits & names & contact info for all witnesses long before this.

Does your husband have a lawyer? If not, sometimes the lack of prep on both sides can cancel each other out & the court may allow you to proceed even when neither of you has done what you were supposed to prior to trial.

However, if he has a lawyer who is even minimally prepared, and you/your lawyer have done nothing, this could go very badly, with near-permanent consequences.

Overly dramatic & badly prepared seems to describe many family law attorneys, sad to say. I would trust your instincts and try to find someone else, who can then move to continue the trial, pointing out that she/he has just been retained. If you can borrow for the fee or do a payment agreement over time, it will often be worth it. (I will be paying for years and it was well worth it.)

But then -- see if your new lawyer can recommend a good mediator who will be favorably inclined to your side of the case, and see if this cannot be settled short of trial. Trial will likely be tremendously expensive.

If you DO end up going to trial ill-prepared, make sure you/your lawyer keeps hitting the refrain that, even if you technically did not provide adequate notice of witnesses or exhibits, the touchstone is the best interests of the child, & the court should hear all evidence that bears on the best interests of the child, even if you technically forfeited the right to introduce it by missing discovery deadlines.

This sounds miserable. Best of luck, but don't rely on luck. Get prepared, even if at the 11th hour. Get a lawyer you feel better about, if you possibly can swing it even by taking on debt to friends or family.