Yes, you should make the payments on the assigned dates. The IRS has a pay as you go system. If you were to wait until the end of the year, you may be liable for a penalty, not to speak of a tax liability it would be difficult to pay. The easy way, without too much fuss, is to on March 31, look at your SE income and figure tax at around 25-30% and send it in. Do the same for the earnings from April-June, etc. You are taxed for SE purposes at 15.3% and for federal by whatever tax bracket you fall into.
