Perhaps you would agree that if someone loves someone else, that love would not include him forcing his will on the other. And while it is certainly true that the Lord wills to save everyone, he does not force us to accept his. God is not a slave driver, he is Love and love invites us to freely accept his offer of an eternal relationship. 
 
While some think that everyone wants to go to heaven, generally they have a heaven in mind of their own design. But the real heaven is not merely a human paradise; it is the Kingdom of God and all its fullness. In heaven is celebrated: Charity, worship of God, truth, chastity, forgiveness, esteem of the poor, humility etc. And yet there are many who reject some or all of these values. Why would a loving God force people to enter into the eternal place which celebrates things they reject? 
 
Hence, the existence of Hell is not opposed to God's love. It is in conformity with the respect necessary for our freedom to accept or reject the relationship of love. Mysteriously, many come to a place in their life where they definitively reject God, and the values of the Kingdom he offers.

You are quoting Romans 6:10 which says, "the death he died, he died to sin, once for all.” In saying that Christ “died to sin,” St. Paul is not saying he died on account of his own personal sins. The Greek word hamartia (Sin), Is often used by St. Paul to refer to our own personal sins. But it is also used to refer in a more collective sense to the sin of the world. For, this fallen world of ours, is immersed in sin, in an attitude of rebellion pride, greed, lust, and so forth. And this climate of sin, is like a force, a mindset, initiated by Satan, and connived in by human beings. It is to this world of sin that Christ died. He broke its back, by dying to it, and rising victorious over it. And he defeated it in the most paradoxical way: he conquered pride, by humility, disobedience by obedience, and death, by dying and rising. 
 
It is to this regime of sin, that Christ died, not his own personal sins of which scripture is clear, he had none. (cf 1 Peter 2: 22) 
 
In the same chapter (6:2, 11), we are taught to realize that we too have died to sin, and that this world of sin is to have no more power over us. We must come to experience increasing power, authority, and victory over the influence of this world of sin. We are to lay hold of the life which Christ offers us wherein this world of sin has no more power over us.

The resurrection accounts in the gospels do have some differences in detail. How many women went out to the tomb that morning, one (Jn 20:21), two (Matt 28:1), or three (Mk 16:1)? How many angels did they see that morning, one (Matt 28:2; Mk 16:5) or two (Lk 24:4; Jn 20:12)? Did the women run to the disciples and tell what they had seen (Mt 28:8; Lk 24:9) or did they say nothing out of fear (Mk 16:8)? Did Jesus see them first in Galilee (Mk 16:7; Mt 28:9) or in Jerusalem (Lk 24:36)? Among the Apostles, did he appear to Peter first (Lk 24:34), all eleven at once (Mt. 28:16), or the eleven minus Thomas (Jn 20:24)? Did Jesus appear to them in a room (Jn 20:19) or a mountaintop (Mt 28:16)? Lastly, did Jesus ascend on Easter Sunday (Lk 24:50-53; Mk 16:19) or forty days later (Acts 1:3-9)? 
 
Most of these apparent discrepancies are not actual conflicts upon closer examination and are easily explained. We cannot look at them all in a short column. But as to your specific question, it would seem most likely that several women went out that morning. That John only focuses on Magdalene is not a denial that others were there. Matthew and Mark, in saying two or three may not be engaging in a headcount per se, but engaging in generalization, such as when we say words like, couple or several. 
 
We should not be surprised that there are some differences in the accounts. Even today, eyewitnesses of an event often emphasize certain details and have different recollections as to the particulars. People often summarize longer stories as well and speak only of essentials. This does not mean that the event did not happen or that unmentioned details by one person is in conflict with details mentioned by another. Given the numerous times Jesus appeared and the many people who saw him, we should not be surprised to find certain differences in the accounts. In this light the differences actually lend credibility to the gospel accounts, which do not try to paper over them, but realistically report them. (See Catechism #s 642-643)