Answer
You may receive the Eucharist twice in one day provided the second reception is within a eucharistic celebration in which you "participate." This is understood to mean the standard level of participation of one attending Mass. The Code of Canon Law states, "A person who has already received the Most Holy Eucharist can receive it a second time on the same day only within the eucharistic celebration in which the person participates, without prejudice to the prescript of can. 921 §2" (CIC 917). (Note: Canon 921 §2 deals with reception by those in danger of death.)
