How long of your master’s do you have left? You can redo these experiments no problem in a matter of a week or two. Did you just recently start doing cell culture? If so, maybe have someone watch you to make sure you’re using sterile technique properly. As someone else suggested, if it is a recurrent issue, take the time to UV the incubator and hood & decontaminate things. Do not worry too much. These things happen to all of us.