Basically you can't, not from the NS. As you noticed, e-tickets can only be paid for using the iDeal system available to Dutch banks' customers, not with (international) credit cards. The only solution available for train journeys in the Netherlands is to book through a third party. Both the Belgium National Railway company and trainline sell tickets between Utrecht and Schiedam Centrum for €12.20.
Buying from the NS at the station would cost you about the same: €11 pay-as-you-go fare to which you have to add a €1 charge for a disposable chip card and €0.5 credit card fee. Buying from a desk is also possible but comes with an extra service charge.
Note that there is no penalty for buying a ticket at the last minute, no seat reservation and all tickets are in principle valid on all trains. Think of the Dutch train network as a glorified public transit network rather than as a long-distance train network like those you might be used to in the UK or elsewhere.
No matter what you do, the bus leg (or the metro when it will be available later this year) will have to be paid for separately. I would recommend buying a regular 1-hour ticket from the driver. If you stay longer in the Netherlands or plan on coming back, buying an anonymous OV-chipkaart might also makes sense but the system is not very visitor-friendly (and deliberately so).
Finally, note that to make things even more confusing the NS website is able to provide public transportation routes to most places in the Netherlands (not only train stations). That doesn't mean NS tickets are valid on bus or trams, you still need to buy a ticket from the relevant local transit company.