In very simple terms, an offer (which includes quotations and estimate - there is no distinction between the two, only how the offer is worded), can be withdrawn at any time until it has been accepted (there are exceptions to this rule like, for example, where this is consideration to keep the offer open for a set period of time). Once the offer has been accepted (and the acceptance must be unequivocal), then a binding contract comes into place, at which point you are obliged to carry out the work / supply the goods, and failure to do so will be a fundamental breach of contract which would allow the 'innocent' party to pursue damages (ie, any increase in the price for obtaining the replacement contractor / supplier).
Therefore, providing your quotation has not been accepted, you can withdraw it.