Don't make PR steps skippable

In a prior issue I mentioned that I was at step 3, mentioning which participants I wanted to invite. I did this but I couldn't click on review because apparently, as I've learnt now with trial and error, in step 1 I didn't indicate when the survey should take place. This confused me and took a lot of time to actually understand that I needed to go back. Ideally I should not be able to progress to the next step if I haven't satisfied all required conditions in the prior step.