You can put another coat of gel stain in a darker color over the top. The gel stain will act as a glaze and you can wipe as much off as you like to get the darkness you desire. Between the SealCoat and the gel stain, you have pretty much sealed the wood, however you can use more gel stain over it. I would put a coat of SealCoat over what you have done and then follow up with an application or two if needed, with a darker gel stain. Depending on the topcoat you will be using, you may want to apply another coat of SealCoat over the darker gel stain before the final applications of your topcoat.